Silver halide light sensitive emulsion layer having enhanced photographic sensitivity

ABSTRACT

A photographic element comprises at least one silver halide emulsion layer in which the silver halide is sensitized with a compound of formula 
     
         Z-(L-XY).sub.k 
    
     wherein: 
     Z is a light absorbing group; 
     L is a linking group containing a least one C, N, S, or O atom; and 
     k is 1 or 2; and 
     XY represents a fragmentable electron donor moiety wherein: 
     1) XY has a an oxidation potential between 0 and about 1.4 V; 
     2) X is an electron donor group; 
     3) Y is a leaving group other than hydrogen; and 
     4) the oxidized form of XY undergoes a bond cleavage reaction to give the radical X.sup.•  and the leaving fragment Y. 
     In a preferred embodiment the radical X.sup.•  has an oxidation potential of ≦-0.7 V.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of application Ser. No. 08/592,166, filedJan. 26, 1996, abandoned, entitled "Silver Halide Light SensitiveEmulsion Having Enhanced Photographic Sensitivity" by Samir Farid etal., the entire disclosures of which are incorporated herein byreference.

FIELD OF THE INVENTION

This invention relates to a photographic element comprising at least onelight sensitive silver halide emulsion layer which has enhancedphotographic sensitivity.

BACKGROUND OF THE INVENTION

A variety of techniques have been used to improve the light-sensitivityof photographic silver halide materials.

Chemical sensitizing agents have been used to enhance the intrinsicsensitivity of silver halide. Conventional chemical sensitizing agentsinclude various sulfur, gold, and group VIII metal compounds.

Spectral sensitizing agents, such as cyanine and other polymethine dyes,have been used alone, or in combination, to impart spectral sensitivityto emulsions in specific wavelength regions. These sensitizing dyesfunction by absorbing long wavelength light that is essentiallyunabsorbed by the silver halide emulsion and using the energy of thatlight to cause latent image formation in the silver halide.

Many attempts have been made to further increase the spectralsensitivity of silver halide materials. One method is to increase theamount of light captured by the spectral sensitizing agent by increasingthe amount of spectral sensitizing agent added to the emulsion. However,a pronounced decrease in photographic sensitivity is obtained if morethan an optimum amount of dye is added to the emulsion. This phenomenonis known as dye desensitization and involves sensitivity loss in boththe spectral region wherein the sensitizing dye absorbs light, and inthe light sensitive region intrinsic to silver halide. Dyedesensitization has been described in The Theory of the PhotographicProcess, Fourth Edition, T. H. James, Editor, pages 265-266, (Macmillan,1977).

It is also known that the spectral sensitivity found for certainsensitizing dyes can be dramatically enhanced by the combination with asecond, usually colorless organic compound that itself displays nospectral sensitization effect. This is known as the supersensitizingeffect.

Examples of compounds which are conventionally known to enhance spectralsensitivity include sulfonic acid derivatives (U.S. Pat. Nos. 2,937,089and 3,706,567), triazine compounds described in U.S. Pat. Nos. 2,875,058and 3,695,888, mercapto compounds described in U.S. Pat. No. 3,457,078,thiourea compounds described in U.S. Pat. No. 3,458,318, pyrimidinederivatives described in U.S. Pat. No. 3,615,632, dihydropyridinecompounds described in U.S. Pat. No. 5,192,654, aminothiatriazoles asdescribed in U.S. Pat. No. 5,306,612 and hydrazines as described in U.S.Pat. Nos. 2,419,975, 5,459,052 and 4,971,890 and European PatentApplication No. 554,856 A1. The sensitivity increases obtained withthese compounds generally are small, and many of these compounds havethe disadvantage that they have the undesirable effect of deterioratingthe stability of the emulsion or increasing fog.

Various electron donating compounds have also been used to improvespectral sensitivity of silver halide materials. U.S. Pat. No. 3,695,588discloses that the electron donor ascorbic acid can be used incombination with a specific tricarbocyanine dye to enhance sensitivityin the infrared region. The use of ascorbic acid to give spectralsensitivity improvements when used in combination with specific cyanineand merocyanine dyes is also described in U.S. Pat. No. 3,809,561,British Patent No. 1,255,084, and British Patent No. 1,064,193. U.S.Pat. No. 4,897,343 discloses an improvement that decreases dyedesensitization by the use of the combination of ascorbic acid, a metalsulfite compound, and a spectral sensitizing dye.

Electron-donating compounds that are convalently attached to asensitizing dye or a silver-halide adsorptive group have also been usedas supersensitizing agents. U.S. Pat. Nos. 5,436,121 and 5,478,719disclose sensitivity improvements with the use of compounds containingelectron-donating styryl bases attached to monomethine dyes. Spectralsensitivity improvements are also described in U.S. Pat. No. 4,607,006for compounds containing an electron-donative group derived from aphenothiazine, phenoxazine, carbazole, dibenzophenothiazine, ferrocene,tris(2,2'-bipyridyl)ruthenium, or a triarylamine skeleton which areconnected to a silver halide adsorptive group. However, most of theselatter compounds have no silver halide sensitizing effect of their ownand provide only minus-blue sensitivity improvements when used incombination with a sensitizing dye.

In our co-pending application filed concurrently herewith (attorney'sdocket No. 69500), we have disclosed a new class of organic electrondonating compounds that, when incorporated into a silver halideemulsion, provide a sensitizing effect alone or in combination withdyes. These compounds donate at least one electron and are fragmentable,i.e., they undergo a bond cleavage reaction other than deprotonation. Inthis application we describe the attachment of such electron donors tosensitizing dyes. The attachment of such electron donors to sensitizingdyes would promote adhesion to the silver halide grain surface. Becausesensitizing dyes are required to be present to impart spectralsensitivity in specific spectral regions, use of a sensitizing dye asthe adsorbing moiety allows the fragmentable electron donating compoundto be close to the surface of the silver halide without displacing thespectral sensitizing agent.

Problem to be Solved by the Invention

There is a continuing need for materials which, when added tophotographic emulsions, increase their sensitivity. Ideally suchmaterials should be usable with a wide range of emulsion types, theiractivity should be controllable and they should not increase fog beyondacceptable limits. This invention provides such materials.

SUMMARY OF THE INVENTION

We have now discovered that attachment of materials which improvesensitivity of photographic emulsions to a spectral sensitizing dyeprovides the added advantage of increased emulsion efficiency atrelatively low concentrations.

In accordance with this invention, a silver halide emulsion layer of aphotographic element is sensitized with a fragmentable electron donormoiety that upon donating an electron, undergoes a bond cleavagereaction other than deprotonation. The term "sensitization" is used inthis patent application to mean an increase in the photographic responseof the silver halide emulsion layer of a photographic element. The term"sensitizer" is used to mean a compound that provides sensitization whenpresent in a silver halide emulsion layer.

One aspect of this invention comprises a photographic element comprisingat least one silver halide emulsion layer in which the silver halide issensitized with a compound of the formula:

    Z-(L-XY).sub.k

wherein Z is a light absorbing group including for example cyanine dyes,complex cyanine dyes, merocyanine dyes, complex merocyanine dyes,homopolar cyanine dyes, styryl dyes, oxonol dyes, hemioxonol dyes, andhemicyanine dyes, and L represents a linking group containing at leastone C, N, S or O atom, k is 1 or 2 and XY is a fragmentable electrondonor moiety in which X is an electron donor group and Y is a leavinggroup other than hydrogen, and wherein:

1) XY has an oxidation potential between 0 and about 1.4 V; and

2) the oxidized form of XY undergoes a bond cleavage reaction to givethe radical X.sup.• and the leaving fragment Y.

Another aspect of this invention comprises a photographic elementcomprising at least one silver halide emulsion layer in which the silverhalide is sensitized with a compound of the formula:

    Z-(L-XY).sub.k

wherein Z is a light adsorbing group including for example cyanine dyes,complex cyanine dyes, merocyanine dyes, complex merocyanine dyes,homopolar cyanine dyes, styryl dyes, oxonol dyes, hemioxonol dyes, andhemicyanine dyes, and L represents a linking group containing at leastone C, N, S or O atom and XY is a fragmentable electron donor moiety inwhich X is an electron donor group, k is 1 or 2 and Y is a leaving groupother than hydrogen, and wherein:

1) XY has an oxidation potential between 0 and about 1.4 V;

2) the oxidized form of XY undergoes a bond cleavage reaction to givethe radical X.sup.• and the leaving fragment Y; and

3) the radical X.sup.• has an oxidation potential ≦-0.7 V (that is,equal to or more negative than about -0.7 V).

Compounds which meet criteria (1) and (2) but not (3) are capable ofdonating one electron and are referred to herein as fragmentableone-electron donors. Compounds which meet all three criteria are capableof donating two electrons and are referred to herein as fragmentabletwo-electron donors.

In this patent application, oxidation potentials are reported as "V"which represents "volts versus a saturated calomel reference electrode".

ADVANTAGEOUS EFFECT OF THE INVENTION

This invention provides a silver halide photographic emulsion containingan organic electron donor capable of enhancing both the intrinsic andspectral sensitivity of the silver halide emulsion. The activity ofthese compounds can be easily varied with substituents to control theirspeed and fog effects in a manner appropriate to the particular silverhalide emulsion in which they are used. An important feature of thesecompounds is that they contain a sensitizing dye moiety, so as tominimize the amount of additive needed to produce a beneficial effect inthe emulsion.

DETAILED DESCRIPTION OF THE INVENTION

The photographic element of this invention comprises a silver halideemulsion layer which contains a fragmentable electron donatingsensitizer molecule represented by the formula:

    Z-(L-XY).sub.k

which when added to a silver halide emulsion, alone or in combinationwith a second spectral sensitizing dye, can increase the photographicsensitivity of the silver halide emulsion. The molecule Z-(L-XY)_(k) iscomprised of three parts:

The linkage group represented by L which connects the light absorbinggroup to the fragmentable electron donating group XY by a covalent bondis preferably an organic linking group containing a least one C, N, S,or O atom. It is also desired that the linking group not be completelyaromatic or unsaturated, so that a pi-conjugation system cannot existbetween the Z and XY moieties. Preferred examples of the linkage groupinclude, an alkylene group, an arylene group, --O--, --S--, --C═O, --SO₂--, --NH--, --P═O, and --N═. Each of these linking components can beoptionally substituted and can be used alone or in combination. Examplesof preferred combinations of these groups are: ##STR1## where c=1-30,and d=1-10

The length of the linkage group can be limited to a single atom or canbe much longer, for instance up to 30 atoms in length. A preferredlength is from about 2 to 20 atoms, and most preferred is 3 to 10 atoms.Some preferred examples of L can be represented by the general formulaeindicated below: ##STR2## e and f=1-30, with the proviso that e+f≦30

Z is a light absorbing group, preferably a spectral sensitizing dyetypically used in color sensitization technology, including for examplecyanine dyes, complex cyanine dyes, merocyanine dyes, complexmerocyanine dyes, homopolar cyanine dyes, styryl dyes, oxonol dyes,hemioxonol dyes, and hemicyanine dyes. Representative spectralsensitizing dyes are discussed in Research Disclosure, Item 36544,September 1994, the disclosure of which, including the disclosure ofreferences cited therein are incorporated herein by reference. Thesedyes may be synthesized by those skilled in the art according to theprocedures described herein or F. M. Hamer, The Cyanine Dyes and RelatedCompounds (Interscience Publishers, New York, 1964). Particularlypreferred as a light absorbing group is a cyanine or merocyanine dyerepresented by the general formulae VIII-XII below: ##STR3## wherein: E₁and E₂ represent the atoms necessary to form a substituted orunsubstituted hetero ring and may be the same or different,

each J independently represents a substituted or unsubstituted methinegroup,

q is a positive integer of from 1 to 4,

p and r each independently represents 0 or 1,

D₁ and D₂ each independently represents substituted or unsubstitutedalkyl or unsubstituted aryl, and

W₂ is a counterion as necessary to balance the charge; ##STR4## whereinE₁, D₁, J, p, q and W₂ are as defined above for formula (VIII) and Grepresents ##STR5## wherein E₄ represents the atoms necessary tocomplete a substituted or unsubstituted heterocyclic nucleus, and F andF' each independently represents a cyano radical, an ester radical, anacyl radical, a carbamoyl radical or an alkylsulfonyl radical; ##STR6##wherein D₁, E₁, J, p, q and W₂ are as defined above for formula (VIII),and G₂ represents a substituted or unsubstituted amino radical or asubstituted or unsubstituted aryl radical; ##STR7## wherein D₁, E₁, D₂,E₁, J, p, q, r and W₂ are as defined for formula (VIII) above, and E₃ isdefined the same as E₄ for formula (IX) above; ##STR8## wherein D₁, E₁,J, G, p, q, r and W₂ are as defined above for formula (VIII) above andE₃ is as defined for formula (XI) above.

In the above formulas, E₁ and E₂ each independently represents the atomsnecessary to complete a substituted or unsubstituted 5- or 6-memberedheterocyclic nucleus. These include a substituted or unsubstituted:thiazole nucleus, oxazole nucleus, selenazole nucleus, quinolinenucleus, tellurazole nucleus, pyridine nucleus, thiazoline nucleus,indoline nucleus, oxadiazole nucleus, thiadiazole nucleus, or imidazolenucleus. This nucleus may be substituted with known substituents, suchas halogen (e.g., chloro, fluoro, bromo), alkoxy (e.g., methoxy,ethoxy), substituted or unsubstituted alkyl (e.g., methyl,trifluoromethyl), substituted or unsubstituted aryl, substituted orunsubstituted aralkyl, sulfonate, and others known in the art.

In one embodiment of the invention, when dyes according to formula(VIII) are used E₁ and E₂ each independently represent the atomsnecessary to complete a substituted or unsubstituted thiazole nucleus, asubstituted or unsubstituted selenazole nucleus, a substituted orunsubstituted imidazole nucleus, or a substituted or unsubstitutedoxazole nucleus.

Examples of useful nuclei for E₁ and E₂ include: a thiazole nucleus,e.g., thiazole, 4-methylthiazole, 4-phenylthiazole, 5-methylthiazole,5-phenylthiazole, 4,5-dimethyl-thiazole, 4,5-diphenylthiazole,4-(2-thienyl)thiazole, benzothiazole, 4-chlorobenzothiazole,5-chlorobenzothiazole, 6-chlorobenzothiazole, 7-chlorobenzothiazole,4-methylbenzothiazole, 5-methylbenzothiazole, 6-methylbenzothiazole,5-bromobenzothiazole, 6-bromobenzothiazole, 5-phenylbenzothiazole,6-phenylbenzothiazole, 4-methoxybenzothiazole, 5-methoxybenzothiazole,6-methoxybenzothiazole, 4-ethoxybenzothiazole, 5-ethoxybenzothiazole,tetrahydrobenzothiazole, 5,6-dimethoxybenzothiazole,5,6-dioxymethylbenzothiazole, 5-hydroxybenzothiazole,6-5-dihydroxybenzothiazole, naphtho[2,1-d]thiazole,5-ethoxynaphtho[2,3-d]thiazole, 8-methoxynaphtho[2,3-d]thiazole,7-methoxynaphtho[2,3-d]thiazole, 4'-methoxythianaphtheno-7',6'-4,5-thiazole, etc.; an oxazole nucleus, e.g., 4-methyloxazole,5-methyloxazole, 4-phenyloxazole, 4,5-diphenyloxazole, 4-ethyloxazole,4,5-dimethyloxazole, 5-phenyloxazole, benzoxazole, 5-chlorobenzoxazole,5-methylbenzoxazole, 5-phenylbenzoxazole, 6-methylbenzoxazole,5,6-dimethylbenzoxazole, 4,6-dimethylbenzoxazole, 5-ethoxybenzoxazole,5-chlorobenzoxazole, 6-methoxybenzoxazole, 5-hydroxybenzoxazole,6-hydroxybenzoxazole, naphtho[2,1-d]oxazole, naphtho[1,2-d]oxazole,etc.; a selenazole nucleus, e.g., 4-methylselenazole,4-phenylselenazole, benzoselenazole, 5-chlorobenzoselenazole,5-methoxybenzoselenazole, 5-hydroxybenzoselenazole,tetrahydrobenzoselenazole, naphtho[2,1-d]selenazole,naphtho[1,2-d]selenazole, etc.; a pyridine nucleus, e.g., 2-pyridine,5-methyl-2-pyridine, 4-pyridine, 3-methyl-4-pyridine,3-methyl-4-pyridine, etc.; a quinoline nucleus, e.g., 2-quinoline,3-methyl-2-quinoline, 5-ethyl-2-quinoline, 6-chloro-2-quinoline,8-chloro-2-quinoline, 6-methoxy-2-quinoline, 8-ethoxy-2-quinoline,8-hydroxy-2-quinoline, 4-quinoline, 6-methoxy-4-quinoline,7-methyl-4-quinoline, 8-chloro-4-quinoline, etc.; a tellurazole nucleus,e.g., benzotellurazole, naphtho[1.2-d]benzotellurazole,5,6-dimethoxybenzotellurazole, 5-methoxybenzotellurazole,5-methylbenzotellurazole; a thiazoline nucleus, e.g.,thiazoline,4-methylthiazoline, etc.; a benzimidazole nucleus, e.g., benzimidazole,5-trifluoromethylbenzimidazole, 5,6-dichlorobenzimidazole; and indolenucleus, 3,3-dimethylindole, 3,3-diethylindole, 3,3,5-trimethylindole;or a diazole nucleus, e.g., 5-phenyl-1,3,4-oxadiazole,5-methyl-1,3,4-thiadiazole.

F and F' are each a cyano radical, an ester radical such as ethoxycarbonyl, methoxycarbonyl, etc., an acyl radical, a carbamoyl radical,or an alkylsulfonyl radical such as ethylsulfonyl, methylsulfonyl, etc.Examples of useful nuclei for E₄ include a 2-thio-2,4-oxazolidinedionenucleus (i.e., those of the 2-thio-2,4-(3H,5H)-oxaazolidinone series)(e.g., 3-ethyl-2-thio-2,4 oxazplidinedione, 3-(2-sulfoethyl)-2-thio-2,4oxazolidinedione, 3-(4-sulfobutyl)-2-thio-2,4 oxazolidinedione,3-(3-carboxypropyl)-2-thio-2,4 oxazolidinedione, etc.; a thianaphthenonenucleus (e.g., 2-(2H)-thianaphthenone, etc.), a2-thio-2,5-thiazolidinedione nucleus (i.e., the2-thio-2,5-(3H,4H)-thiazoledeione series) (e.g.,3-ethyl-2-thio-2,5-thiazolidinedione, etc.); a 2,4-thiazolidinedionenucleus (e.g., 2,4-thiazolidinedione, 3-ethyl-2,4-thiazolidinedione,3-phenyl-2,4-thiazolidinedione, 3-α-naphthyl-2,4-thiazolidinedione,etc.); a thiazolidinone nucleus (e.g., 4-thiazolidinone,3-ethyl-4-thiazolidinone, 3-phenyl-4-thiazolidinone,3-α-naphthyl-4-thiazolidinone, etc.); a 2-thiazolin-4-one series (e.g.,2-ethylmercapto-2-thiazolin-4-one, 2-alkylphenyamino-2-thiazolin-4-one,2-diphenylamino-2-thiazolin-4-one, etc.) a 2-imino-4-oxazolidinone(i.e., pseudohydantoin) series (e.g., 2,4-imidazolidinedione (hydantoin)series (e.g., 2,4-imidazolidinedione, 3-ethyl-2,4-imidazolidinedione,3-phenyl-2,4-imidazolidinedione, 3-α-naphthyl-2,4-imidazolidinedione,1,3-diethyl-2,4-imidazolidinedione,1-ethyl-3-phenyl-2,4-imidazolidinedione,1-ethyl-2-α-naphthyl-2,4-imidazolidinedione,1,3-diphenyl-2,4-imidazolidinedione, etc.); a2-thio-2,4-imidazolidinedione (i.e., 2-thiohydantoin) nucleus (e.g.,2-thio-2,4-imidazolidinedione, 3-ethyl-2-thio-2,4-imidazolidinedione,3-(2-carboxyethyl)-2-thio-2,4-imidazolidinedione,3-phenyl-2-thio-2,4-imidazolidinedione,1,3-diethyl-2-thio-2,4-imidazolidinedione,1-ethyl-3-phenyl-2-thio-2,4-imidazolidinedione,1-ethyl-3-naphthyl-2-thio-2,4-imidazolidinedione,1,3-diphenyl-2-thio-2,4-imidazolidinedione, etc.); a 2-imidazolin-5-onenucleus.

G₂ represents a substituted or unsubstituted amino radical (e.g.,primary amino, anilino), or a substituted or unsubstituted aryl radical(e.g., phenyl, naphthyl, dialkylaminophenyl, tolyl, chlorophenyl,nitrophenyl).

According to the formulas (VIII)-(XII), each J represents a substitutedor unsubstituted methine group. Examples of substituents for the methinegroups include alkyl (preferably of from 1 to 6 carbon atoms, e.g.,methyl, ethyl, etc.) and aryl (e.g., phenyl). Additionally, substituentson the methine groups may form bridged linkages.

W₂ represents a counterion as necessary to balance the charge of the dyemolecule. Such counterions include cations and anions for examplesodium, potassium, triethylammonium, tetramethylguanidinium,diisopropylammonium and tetrabutylammonium, chloride, bromide, iodide,para-toluene sulfonate and the like.

D₁ and D₂ are each independently substituted or unsubstituted aryl(preferably of 6 to 15 carbon atoms), or more preferably, substituted orunsubstituted alkyl (preferably of from 1 to 6 carbon atoms). Examplesof aryl include phenyl, tolyl, p-chlorophenyl, and p-methoxyphenyl.Examples of alkyl include methyl, ethyl, propyl, isopropyl, butyl,hexyl, cyclohexyl, decyl, dodecyl, etc., and substituted alkyl groups(preferably a substituted lower alkyl containing from 1 to 6 carbonatoms), such as a hydroxyalkyl group, e.g., 2-hydroxyethyl,4-hydroxybutyl, etc., a carboxyalkyl group, e.g., 2-carboxyethyl,4-carboxybutyl, etc., a sulfoalkyl group, e.g., 2-sulfoethyl,3-sulfobutyl, 4-sulfobutyl, etc., a sulfatoalkyl group, etc., anacyloxyalkyl group, e.g., 2-acetoxyethyl, 3-acetoxypropyl,4-butyroxybutyl, etc., an alkoxycarbonlyalkyl group, e.g.,2-methoxycarbonlyethyl, 4-ethoxycarbonylbutyl, etc., or an aralkylgroup, e.g., benzyl, phenethyl, etc., The alkyl or aryl group may besubstituted by one or more of the substituents on the above-describedsubstituted alkyl groups.

Particularly preferred dyes are: ##STR9##

The linking group L may be attached to the dye at one (or more) of theheteroatoms, at one (or more) of the aromatic or heterocyclic rings, orat one (or more) of the atoms of the polymethine chain, at one (or more)of the heteroatoms, at one (or more) of the aromatic or heterocyclicrings, or at one (or more) of the atoms of the polymethine chain. Forsimplicity, and because of the multiple possible attachment sites, theattachment of the L group is not specifically indicated in the genericstructures. Specific structures of illustrative Z-(L-XY)_(k) compoundsare provided below.

Substituent groups in the light absorbing Z or electron donating XYgroups can become part of the linkage group in general formulaZ-(L-XY)_(k).

XY is a fragmentable electron donor moiety wherein X is an electrondonor group and Y is a leaving group. The preparation of compounds ofthe formula X-Y is disclosed in co-pending application Ser. No. - -,filed concurrently herewith (attorney's docket No. 69500), the entiredisclosure of which is incorporated herein by reference. The followingrepresents the reactions believed to take place when the XY moietyundergoes oxidation and fragmentation to produce a radical X.sup.•,which in a preferred embodiment undergoes further oxidation. ##STR10##

The structural features of the moiety XY are defined by thecharacteristics of the two parts, namely the fragment X and the fragmentY. The structural features of the fragment X determines the oxidationpotential of the XY moiety (E₁) and that of the radical X.sup.• (E₂),whereas both the X and Y fragments affect the fragmentation rate of theoxidized moiety XY.sup.•+.

Preferred X groups are of the general formula: ##STR11## The symbol "R"(that is R without a subscript) is used in all structural formulae inthis patent application to represent a hydrogen atom or an unsubstitutedor substituted alkyl group.

In structure (I):

m: 0, 1;

Z: O, S, Se, Te;

Ar: aryl group (e.g., phenyl, naphthyl, phenanthryl, anthryl); orheterocyclic group (e.g., pyridine, indole, benzimidazole, thiazole,benzothiazole, thiadiazole, etc.);

R₁ : R, carboxyl, amide, sulfonamide, halogen, NR₂, (OH)_(n), (OR')_(n)or (SR)_(n) where R' is alkyl or substituted alkyl;

n: 1-3;

R₂ : R, Ar';

R₃ : R, Ar';

R₂ and R₃ together can form 5- to 8- membered ring;

R₂ and Ar: can be linked to form 5- to 8- membered ring;

R₃ and Ar: can be linked to form 5- to 8- membered ring;

Ar': aryl group such as phenyl, substituted phenyl, or heterocyclicgroup (e.g., pyridine, benzothiazole, etc.)

R: a hydrogen atom or an unsubstituted or substituted alkyl group.

In structure (II):

Ar: aryl group (e.g., phenyl, naphthyl, phenanthryl); or heterocyclicgroup (e.g., pyridine, benzothiazole, etc.);

R₄ : a substituent having a Hammett sigma value of -1 to +1, preferably-0.7 to +0.7, e.g., R, OR, SR, halogen, CHO, C(O)R, COOR, CONR₂, SO₃ R,SO₂ NR₂, SO₂ R, SOR, C(S)R, etc;

R₅ : R, Ar'

R₆ and R₇ : R, Ar'

R₅ and Ar: can be linked to form 5- to 8- membered ring;

R₆ and Ar: can be linked to form 5- to 8- membered ring (in which case,R₆ can be a hetero atom);

R₅ and R₆ : can be linked to form 5- to 8- membered ring;

R₆ and R₇ : can be linked to form 5- to 8- membered ring;

Ar': aryl group such as phenyl, substituted phenyl, heterocyclic group

R: hydrogen atom or an unsubstituted or substituted alkyl group.

A discussion on Hammett sigma values can be found in C. Hansch and R. W.Taft Chem. Rev. Vol 91, (1991) p 165, the disclosure of which isincorporated herein by reference.

In structure (III):

W=O, S, Se;

Ar: aryl group (e.g., phenyl, naphthyl, phenanthryl, anthryl); orheterocyclic group (e.g., indole, benzimidazole, etc.)

R₈ : R, carboxyl, NR₂, (OR)_(n), or (SR)_(n) (n=1-3);

R₉ and R₁₀ : R, Ar';

Ar': aryl group such as phenyl, substituted phenyl, or heterocyclicgroup (e.g., pyridine, benzothiazole, etc.)

R₉ and Ar: can be linked to form 5- to 8- membered ring;

R: a hydrogen atom or an unsubstituted or substituted alkyl group.

In structure (IV):

"ring" represents a substituted or unsubstituted 5-, 6- or 7-memberedunsaturated ring, preferrably a heterocyclic ring.

Since X is an electron donor group (i.e., an electron rich organicgroup), the substituents on the aromatic groups (Ar and/or Ar'), for anyparticular X group should be selected so that X remains electron rich.For example, if the aromatic group is highly electron rich, e.g.anthracene, electron withdrawing substituents can be used, providing theresulting XY moiety has an oxidation potential of 0 to about 1.4 V.Conversely, if the aromatic group is not electron rich, electrondonating substituents should be selected.

When reference in this application is made to a substituent "group" thismeans that the substituent may itself be substituted or unsubstituted(for example "alkyl group" refers to a substituted or unsubstitutedalkyl). Generally, unless otherwise specifically stated, substituents onany "groups" referenced herein or where something is stated to bepossibly substituted, include the possibility of any groups, whethersubstituted or unsubstituted, which do not destroy properties necessaryfor the photographic utility. It will also be understood throughout thisapplication that reference to a compound of a particular general formulaincludes those compounds of other more specific formula which specificformula falls within the general formula definition. Examples ofsubstituents on any of the mentioned groups can include knownsubstituents, such as: halogen, for example, chloro, fluoro, bromo,iodo; alkoxy, particularly those with 1 to 12 carbon atoms (for example,methoxy, ethoxy); substituted or unsubstituted alkyl, particularly loweralkyl (for example, methyl, trifluoromethyl); alkenyl or thioalkyl (forexample, methylthio or ethylthio), particularly either of those with 1to 12 carbon atoms; substituted and unsubstituted aryl, particularlythose having from 6 to 20 carbon atoms (for example, phenyl); andsubstituted or unsubstituted heteroaryl, particularly those having a 5-or 6-membered ring containing 1 to 3 heteroatoms selected from N, O, orS (for example, pyridyl, thienyl, furyl, pyrrolyl); and others known inthe art. Alkyl substituents preferably contain 1 to 12 carbon atoms andspecifically include "lower alkyl", that is,having from 1 to 6 carbonatoms, for example, methyl, ethyl, and the like. Further, with regard toany alkyl group, alkylene group or alkenyl group, it will be understoodthat these can be branched or unbranched and include ring structures.

The linking group L is usually attached to the X group of the XY moiety,although in certain circumstances, may be attached to the Y group (seebelow). The L group may be attached to X at any of the substituents R₁-R₁₀, or to the aryl group of X in structures (I)-(III), or to the ringin structure (IV). Illustrative examples of preferred X groups are givenbelow. For simplicity and because of the multiple possible sites, theattachment of the L group is not specifically indicated in thestructures. Specific structures for linked Z-L-XY compounds are providedhereinafter.

The following are illustrative examples of the group X of generalstructure I: ##STR12##

In the structures of this patent application a designation such as--OR(NR₂) indicates that either --OR or --NR₂ can be present.

The following are illustrative examples of the group X of generalstructure II: ##STR13##

The following are illustrative examples of the group X of the generalstructure III: ##STR14##

The following are illustrative examples of the group X of the generalstructure IV: ##STR15##

Preferred Y groups are:

(1) X', where X' is an X group as defined in structures I-IV and may bethe same as or different from the X group to which it is attached

(2) ##STR16## (3) ##STR17## where M=Si, Sn or Ge; and R'=alkyl orsubstituted alkyl (4) ##STR18## where Ar"=aryl or substituted aryl

The linking group L may be attached to the Y group in the case of (3)and (4). For simplicity, the attachment of the L group is notspecifically indicated in the generic formulae.

In preferred embodiments of this invention Y is COO⁻ or Si(R')₃ or an Xgroup. Particularly preferred Y groups are COO⁻ or Si(R')₃.

Preferred XY moieties are derived from X-Y compounds of the formulaegiven below (for simplicity, the multiple possible sites, the the Lgroup is not specified):

    ______________________________________                                         ##STR19##                                                                    Cpd. No.      R.sub.17  R.sub.18   R.sub.19                                   ______________________________________                                        1             CH.sub.3  H          H                                          2             C.sub.2 H.sub.5                                                                         OH         H                                          3             CH.sub.3  OH         H                                          4             C.sub.2 H.sub.5                                                                         OH         CH.sub.3                                   5             CH.sub.3  OH         CH.sub.3                                   6             C.sub.2 H.sub.5                                                                         OCH.sub.3  CH.sub.3                                   7             CH.sub.3  OCH.sub.3  CH.sub.3                                   8             C.sub.2 H.sub.5                                                                         OCH.sub.3  H                                          ______________________________________                                    

    ______________________________________                                         ##STR20##                                                                    Cpd. No.  R.sub.20    R.sub.21 R.sub.22                                                                            R.sub.23                                 ______________________________________                                         9        OCH.sub.2 CO.sub.2.sup.-                                                                  H        H     H                                        10        OCH.sub.3   H        H     H                                        11        CH.sub.3    H        H     H                                        12        Cl          H        H     H                                        13        H           H        H     H                                        14        H           H        CH.sub.3                                                                            H                                        15        OCH.sub.3   H        CH.sub.3                                                                            H                                        16        CH(CH.sub.3)C.sub.2 H.sub.5                                                               H        CH.sub.3                                                                            H                                        17        CHO         H        CH.sub.3                                                                            H                                        18        SO.sub.3.sup.-                                                                            H        CH.sub.3                                                                            H                                        19        SO.sub.2 N(C.sub.2 H.sub.5).sub.2                                                         H        CH.sub.3                                                                            H                                        20        CH.sub.3    H        CH.sub.3                                                                            H                                        21        OCH.sub.3   OCH.sub.3                                                                              H     H                                        22        H           H        H     OCH.sub.2 CO.sub.2.sup.-                 ______________________________________                                    

    ______________________________________                                         ##STR21##                                                                    Cpd. No.  R.sub.20  R.sub.22  R.sub.24 R.sub.21                               ______________________________________                                        23        OCH.sub.3 CH.sub.3  H        H                                      24        H         CH.sub.3  H        H                                      25        CO.sub.2.sup.-                                                                          CH.sub.3  H        H                                      26        Cl        CH.sub.3  H        H                                      27        CONH.sub.2                                                                              CH.sub.3  H        H                                      28        CO.sub.2 C.sub.2 H.sub.5                                                                CH.sub.3  H        H                                      29        CH.sub.3  CH.sub.2 CO.sub.2.sup.-                                                                 H        H                                      30        H         CH.sub.2 CO.sub.2.sup.-                                                                 H        H                                      31        CO.sub.2.sup.-                                                                          CH.sub.2 CO.sub.2.sup.-                                                                 H        H                                      32        H         CH.sub.3  H        CONH.sub.2                             33        CO.sub.2.sup.-                                                                          CH.sub.3  CH.sub.3 H                                      34        H         CH.sub.3  C.sub.2 H.sub.5                                                                        CONH.sub.2                             35        CH.sub.3  CH.sub.3  (CH.sub.2).sub.3 CH.sub.3                                                              H                                      36        OCH.sub.3 CH.sub.3  (CH.sub.2).sub.3 CH.sub.3                                                              H                                      37        H         CH.sub.3  (CH.sub.2).sub.3 CH.sub.3                                                              H                                      38        CO.sub.2.sup.-                                                                          CH.sub.3  (CH.sub.2).sub.3 CH.sub.3                                                              H                                      39        Cl        CH.sub.3  (CH.sub.2).sub.3 CH.sub.3                                                              H                                      40        CH.sub.3  CH.sub.2 CO.sub.2.sup.-                                                                 (CH.sub.2).sub.3 CH.sub.3                                                              H                                      41        H         CH.sub.2 CO.sub.2.sup.-                                                                 (CH.sub.2).sub.3 CH.sub.3                                                              H                                       ##STR22##                                                                     ##STR23##                                                                     ##STR24##                                                                     ##STR25##                                                                     ##STR26##                                                                     ##STR27##                                                                     ##STR28##                                                                     ##STR29##                                                                     ##STR30##                                                                     ##STR31##                                                                     ##STR32##                                                                     ##STR33##                                                                     ##STR34##                                                                     ##STR35##                                                                     ##STR36##                                                                     ##STR37##                                                                    ______________________________________                                    

In the above formulae, counterion(s) required to balance the charge ofthe XY moiety are not shown as any counterion can be utilized. Commoncounterions are sodium, potassium, triethylammonium (TEA⁺),tetramethylguanidinium (TMG⁺), diisopropylammonium (DIPA⁺), andtetrabutylammonium (TBA⁺).

Fragmentable electron donating moieties XY are derived from electrondonating compounds X-Y which can be fragmentable one electron donatingcompounds which meet the first two criteria set forth below orfragmentable two electron donating compounds which meet all threecriteria set forth below. The first criterion relates to the oxidationpotential of X-Y (E₁). E₁ is preferably no higher than about 1.4 V andpreferably less than about 1.0 V. The oxidation potential is preferablygreater than 0, more preferably greater than about 0.3 V. E₁ ispreferably in the range of about 0 to about 1.4 V, and more preferablyof from about 0.3 V to about 1.0 V.

Oxidation potentials are well known and can be found, for example, in"Encyclopedia of Electrochemistry of the Elements", Organic Section,Volumes XI-XV, A. Bard and H. Lund (Editors) Marcel Dekkar Inc., N.Y.(1984). E₁ can be measured by the technique of cyclic voltammetry. Inthis technique, the electron donating compound is dissolved in asolution of 80%/20% by volume acetonitrile to water containing 0.1 Mlithium perchlorate. Oxygen is removed from the solution by passingnitrogen gas through the solution for 10 minutes prior to measurement. Aglassy carbon disk is used for the working electrode, a platinum wire isused for the counter electrode, and a saturated calomel electrode (SCE)is used for the reference electrode. Measurement is conducted at 25° C.using a potential sweep rate of 0.1 V/sec. The oxidation potential vs.SCE is taken as the peak potential of the cyclic voltammetric wave. E₁values for typical X-Y compounds useful in preparing the compounds ofthis invention are given in Table A.

                  TABLE A                                                         ______________________________________                                        Oxidation Potential of X-Y                                                    Compound  E.sub.1  (V vs SCE)                                                                        Compound  E.sub.1  (V vs SCE)                          ______________________________________                                        1         0.53         30        0.60                                         2         0.50         26        0.51                                         5         0.51         27        0.62                                         4         0.49         38        0.48                                         7         0.52         39        0.40                                         6         0.51         41        0.48                                         8         0.49         34        0.52                                         48        0.70         28        0.61                                         51        0.91         17        0.74                                         49        ˜1.2   18        0.70                                         50        ˜1.05  19        0.68                                         43        0.61         31        0.61                                         44        0.64         22        0.65                                         45        0.64         59        0.53                                         46        0.68         56        0.65                                         42        0.30         57        0.49                                         9         0.38         58        0.49                                         10        0.38         52        0.07                                         11        0.46         54        0.44                                         23        0.37                                                                20        0.46                                                                14        0.50                                                                15        0.36                                                                16        0.47                                                                36        0.22                                                                29        0.52                                                                40        0.38                                                                35        0.34                                                                25        0.62                                                                33        0.54                                                                13        0.54                                                                12        0.58                                                                21        0.36                                                                24        0.52                                                                37        0.43                                                                32        0.58                                                                60        0.80                                                                ______________________________________                                    

The second criterion defining the fragmentable XY groups is therequirement that the oxidized form of X-Y, that is the radical cationX-Y⁺•, undergoes a bond cleavage reaction to give the radical X.sup.•and the fragment Y⁺ (or in the case of an anionic compound the radicalX.sup.• and the fragment Y). This bond cleavage reaction is alsoreferred to herein as "fragmentation". It is widely known that radicalspecies, and in particular radical cations, formed by a one-electronoxidation reaction may undergo a multitude-of reactions, some of whichare dependent upon their concentration and on the specific environmentwherein they are produced. As described in "Kinetics and Mechanisms ofReactions of Organic Cation Radicals in Solution", Advances in PhysicalOrganic Chemistry, vol 20, 1984, pp 55-180, and "Formation, Propertiesand Reactions of Cation Radicals in Solution", Advances in PhysicalOrganic Chemistry, vol 13, 1976, pp 156-264, V. Gold Editor, 1984,published by Academic Press, N.Y., the range of reactions available tosuch radical species includes: dimerization, deprotonation, hydrolysis,nucleophilic substitution, disproportionation, and bond cleavage. Withcompounds useful in accordance with our invention, the radical formed onoxidation of X-Y undergoes a bond cleavage reaction.

The kinetics of the bond cleavage or fragmentation reaction can bemeasured by conventional laser flash photolysis. The general techniqueof laser flash photolysis as a method to study properties of transientspecies is well known (see, for example, "Absorption Spectroscopy ofTransient Species". Herkstroeter and I. R. Gould in Physical Methods ofChemistry Series, second Edition, Volume 8, page 225, edited by B.Rossiter and R. Baetzold, John Wiley & Sons, New York, 1993). Thespecific experimental apparatus we used to measure fragmentation rateconstants and radical oxidation potentials is described in detail below.The rate constant of fragmentation in compounds useful in accordancewith this invention is preferably faster than about 0.1 per second(i.e., 0.1 s⁻¹ or faster, or, in other words, the lifetime of theradical cation X-Y⁺• should be 10 sec or less). The fragmentation rateconstants can be considerably higher than this, namely in the 10² to10¹³ s⁻¹ range. The fragmentation rate constant is preferably about 0.1sec⁻¹ to about 10¹³ s⁻¹, more preferably about 10² to about 10⁹ s⁻¹.Fragmentation rate constants k_(fr) (s⁻¹) for typical compounds usefulin accordance with our invention are given in Table B.

                  TABLE B                                                         ______________________________________                                        Rate Constants for Decarboxylation                                            of Radical Cations in CH.sub.3 CN/H.sub.2 O(4:1)                              ______________________________________                                         ##STR38##                                                                    COMP'D  R.sub.26                                                                              R.sub.27                                                                              R.sub.28                                                                             R.sub.29                                                                             k.sub.fr (s.sup.-1)                     ______________________________________                                        14      H       H       Me     CH.sub.2 CO.sub.2.sup.-                                                              >2.0 × 10.sup.7                   13      H       H       H      CH.sub.2 CO.sub.2.sup.-                                                              1.7 × 10.sup.7                    20      Me      H       Me     CH.sub.2 CO.sub.2.sup.-                                                              8.1 × 10.sup.6                    11      Me      H       H      CH.sub.2 CO.sub.2.sup.-                                                              1.6 × 10.sup.6                    15      OMe     H       Me     CH.sub.2 CO.sub.2.sup.-                                                              9.0 × 10.sup.4                    10      OMe     H       H      CH.sub.2 CO.sub.2.sup.-                                                              9.3 × 10.sup.3                    21      OMe     OMe     H      CH.sub.2 CO.sub.2.sup.-                                                                1 × 10.sup.3                    36      OMe     H       Me     n-Bu   1.1 × 10.sup.6                    40      Me      H       CH.sub.2 CO.sub.2.sup.-                                                              n-Bu   1.3 × 10.sup.7                    29      Me      H       CH.sub.2 CO.sub.2.sup.-                                                              H      5.4 × 10.sup.6                    54      Me      H       Me     H      1.4 × 10.sup.7                    ______________________________________                                         ##STR39##                                                                    COMPOUND      R.sub.30 R.sub.31                                                                             k.sub.fr (s.sup.-1)                             ______________________________________                                        3             OH       Me     5.5 × 10.sup.5                            1             H        H      ˜3.0 × 10.sup.5                     ______________________________________                                         ##STR40##                                                                           COMPOUND k.sub.fr (s.sup.-1)                                           ______________________________________                                               47       >10.sup.7                                                     ______________________________________                                         ##STR41##                                                                    COMPOUND          R.sub.32                                                                             k.sub.fr (s.sup.-1)                                  ______________________________________                                        52                H      >10.sup.9                                            53                Et     >10.sup.9                                            ______________________________________                                         ##STR42##                                                                    COMPOUND       k.sub.fr (s.sup.-1)                                            ______________________________________                                        44             5.3 × 10.sup.5                                           ______________________________________                                         ##STR43##                                                                    COMPOUND       k.sub.fr (s.sup.-1)                                            ______________________________________                                        56             1.2 × 10.sup.5                                           ______________________________________                                         ##STR44##                                                                    COMPOUND       k.sub.fr (s.sup.-1)                                            ______________________________________                                        57             ca. 1 × 10.sup.5                                         ______________________________________                                    

In a preferred embodiment of the invention, the XY moiety is afragmentable two-electron donor moiety and meets a third criterion, thatthe radical X.sup.• resulting from the bond cleavage reaction has anoxidation potential equal to or more negative than -0.7 V, preferablymore negative than about -0.9 V. This oxidation potential is preferablyin the range of from about -0.7 to about -2 V, more preferably fromabout -0.8 to about -2 V and most preferably from about -0.9 to about-1.6 V.

The oxidation potential of many radicals have been measured by transientelectrochemical and pulse radiolysis techniques as reported by Wayner,D. D.; McPhee, D. J.; Griller, D. in J. Am. Chem. Soc. 1988, 110, 132;Rao, P. S,; Hayon, E. J. Am. Chem. Soc. 1974, 96, 1287 and Rao, P. S,;Hayon, E. J. Am. Chem. Soc. 1974, 96, 1295. The data demonstrate thatthe oxidation potentials of tertiary radicals are less positive (i.e.,the radicals are stronger reducing agents) than those of thecorresponding secondary radicals, which in turn are more negative thanthose of the corresponding primary radicals. For example, the oxidationpotential of benzyl radical decreases from 0.73 V to 0.37 V to 0.16 Vupon replacement of one or both hydrogen atoms by methyl groups.##STR45##

A considerable decrease in the oxidation potential of the radicals isachieved by α hydroxy or alkoxy substituents. For example the oxidationpotential of the benzyl radical (+0.73 V) decreases to -0.44 when one ofthe α hydrogen atoms is replaced by a methoxy group. ##STR46##

An α-amino substituent decreases the oxidation potential of the radicalto values of about -1 V.

In accordance with our invention we have discovered that compounds whichprovide a radical X.sup.• having an oxidation potential more negativethan -0.7 are particularly advantageous for use in sensitizing silverhalide emulsions. As set forth in the above-noted articles, thesubstitution at the α carbon atom influences the oxidation potential ofthe radical. We have found that substitution of the phenyl moiety withat least one-electron donating substituent or replacement of the phenylwith an electron donating aryl or heterocyclic group also influences theoxidation potential of X.sup.•. Illustrative examples of X.sup.• havingan oxidation potential more negative than -0.7 are given below in TableC. The oxidation potential of the transient species X.sup.•, can bedetermined using a laser flash photolysis technique as described ingreater detail below.

In this technique, the compound X-Y is oxidized by an electron transferreaction initiated by a short laser pulse. The oxidized form of X-Y thenundergoes the bond cleavage reaction to give the radical X.sup.•.X.sup.• is then allowed to interact with various electron acceptorcompounds of known reduction potential. The ability of X.sup.• to reducea given electron acceptor compound indicates that the oxidationpotential of X.sup.• is nearly equal to or more negative than thereduction potential of that electron acceptor compound. The experimentaldetails are set forth more fully below. The oxidation potentials (E₂)for radicals X.sup.• for typical compounds useful in accordance with ourinvention are given in Table C. Where only limits on potentials could bedetermined, the following notation is used: <-0.90 V should be read as"more negative than -0.90 V" and >-0.40 V should be read as "lessnegative than -0.40 V".

Illustrative X.sup.• radicals useful in accordance with the thirdcriterion of our invention are those given below having an oxidationpotential E₂ more negative than -0.7 V. Some comparative examples withE₂ less negative than -0.7 V are also included.

                  TABLE C                                                         ______________________________________                                        Oxidation Potentials of Radicals (X.sup.•), E.sub.2                     ______________________________________                                         ##STR47##                                                                    Parent X-Y                                                                    compound      R.sub.33  R.sub.34                                                                             E.sub.2                                        ______________________________________                                        46            H         H      ˜-0.34                                   45            Me        H      -0.56                                          44            Me        Me     -0.81                                          43            OH        H      -0.89                                          ______________________________________                                         ##STR48##                                                                    Parent X-Y                                                                    compound      R.sub.35  R.sub.36                                                                             E.sub.2                                        ______________________________________                                        13            H         H      ˜-0.85                                   14            H         Me     <-0.9                                          11            Me        H      ˜-0.9                                    16            i-Bu      H      ˜-0.9                                    20            Me        Me     <-0.9                                          10            OMe       H      <-0.9                                          15            OMe       Me     <-0.9                                          ______________________________________                                         ##STR49##                                                                    Parent X-Y                                                                    compound    R.sub.37 R.sub.38 R.sub.39                                                                           E.sub.2                                    ______________________________________                                        8           Et       H        OMe  ˜-0.85                               2           Et       H        OH   <-0.9                                      7           Me       Me       OMe  <-0.9                                      5           Me       Me       OH   <-0.9                                      1           Me       H        H    >-0.5                                      ______________________________________                                         ##STR50##                                                                    Parent X-Y                                                                    compound    R.sub.40 R.sub.41 R.sub.42                                                                           E.sub.2                                    ______________________________________                                        36          OMe      Me       n-Bu <-0.9                                      33          CO.sub.2.sup.-                                                                         Me       Me   <-0.9                                      ______________________________________                                         ##STR51##                                                                    Parent X-Y                                                                    compound    R.sub.44 R.sub.43 R.sub.46                                                                           E.sub.2                                    ______________________________________                                        48          OMe      OMe      OMe  <-0.9                                      51          OMe      H        OMe  <-0.9                                      49          H        H        H    -0.75                                      50          OMe      H        H    <-0.9                                      ______________________________________                                         ##STR52##                                                                           Parent X-Y                                                                            E.sub.2                                                        ______________________________________                                               42      ˜-0.9                                                    ______________________________________                                         ##STR53##                                                                           Parent X-Y                                                                            E.sub.2                                                        ______________________________________                                               47      <-0.9                                                          ______________________________________                                         ##STR54##                                                                    Parent X-Y                                                                    compound         R.sub.32                                                                             E.sub.2                                               ______________________________________                                        52               H      <-0.9                                                 53               Et     <-0.9                                                 ______________________________________                                         ##STR55##                                                                           Parent X-Y                                                                    compound                                                                              E.sub.2                                                        ______________________________________                                               54      <-0.9                                                          ______________________________________                                         ##STR56##                                                                           Parent X-Y                                                                    compound                                                                              E.sub.2                                                        ______________________________________                                               29      <-0.9                                                          ______________________________________                                         ##STR57##                                                                           Parent X-Y                                                                    compound                                                                              E.sub.2                                                        ______________________________________                                               56      <-0.9                                                          ______________________________________                                         ##STR58##                                                                           Parent X-Y                                                                    compound                                                                              E.sub.2                                                        ______________________________________                                               57      <-0.9                                                          ______________________________________                                    

Specific inventive compounds according to the general formulae givenabove are listed below, but the present invention should not beconstrued as being limited thereto. As is demonstrated in theseexamples, the point of attachment of the linking group L to the lightabsorbing group may be at one (or more) of the heteroatoms, at one (ormore) of the aromatic or heterocyclic rings, or at one (or more) of theatoms of the polymethine chain. ##STR59##

Table D combines electrochemical and laser flash photolysis data for theXY moiety contained in selected fragmentable electron donatingsensitizers according to the formula Z-L-XY. Specifically, this Tablecontains data for E₁, the oxidation potential of the parent fragmentableelectron donating moiety X-Y; k_(fr), the fragmentation rate of theoxidized X-Y (including X-Y.sup.•+); and E₂, the oxidation potential ofthe radical X.sup.•. In Table D, these characteristic properties of themoiety XY are reported for the model compound where the dye Z and thelinking group L have been replaced by an unsubstituted alkyl group. Inthe actual compounds Z-L-XY, these characteristic properties may varyslightly from the values for the model compounds but will not be greatlyperturbed. The data in Table D illustrate Z-L-XY compounds useful inthis invention that are fragmentable two-electron donating sensitizersand meet all the three criteria set forth above as well as fragmentableone-electron donating sensitizers useful in this invention that meet thefirst two criteria, but produce a radical X.sup.• having an oxidationpotential E₂ less negative that -0.7 V.

                  TABLE D                                                         ______________________________________                                                E.sub.1  (V) k.sub.fr  (s.sup.-1)                                                                     E.sub.2  (V)                                  Compound                                                                              for XY moiety                                                                              for XY moiety                                                                            for XY moiety                                 ______________________________________                                        Inv 8   0.22         1.1 × 10.sup.6                                                                     <-0.9                                         Inv 9   0.34         6 × 10.sup.7                                                                       <-0.9                                         Inv 11  0.34         6 × 10.sup.7                                                                       <-0.9                                         Inv 12  0.34         6 × 10.sup.7                                                                       <-0.9                                         Inv 10  0.43         >2 × 10.sup.7                                                                      <-0.9                                         Inv 14  0.43         >2 × 10.sup.7                                                                      <-0.9                                         Inv 2   0.55         5.5 × 10.sup.5                                                                     <-0.9                                         Inv 3   0.55         5.5 × 10.sup.5                                                                     <-0.9                                         Inv 6   0.43         >2 × 10.sup.7                                                                      <-0.9                                         Inv 15  0.57         3 × 10.sup.5                                                                       >-0.5                                         ______________________________________                                    

Some comparative compounds similar to the general formulae given aboveare also listed below. The XY component on these comparative compoundsare present as ethyl esters, and do not fragment, and thereby fail tomeet criteria two and three of the invention. ##STR60##

In the above formulae, counterion(s) required to balance the net chargeof a Z-L-XY compound are not shown as any counterion can be utilized.Common counterions that can be used include sodium, potassium,triethylammonium (TEA⁺), tetramethylguanidinium (TMG⁺),diisopropylammonium (DIPA⁺), and tetrabutylammonium (TBA⁺).

The fragmentable electron donors useful in this invention are vastlydifferent from the silver halide adsorptive (one)-electron donorsdescribed in U.S. Pat. No. 4,607,006. The electron donating moietiesdescribed therein, for example phenothiazine, phenoxazine, carbazole,dibenzophenothiazine, ferrocene, tris(2,2'-bipyridyl)ruthenium, or atriarylamine, are well known for forming extremely stable, i.e.,non-fragmentable, radical cations as noted in the following referencesJ. Heterocyclic Chem., vol. 12, 1975, pp 397-399, J. Org. Chem., vol 42,1977, pp 983-988, "The Encyclopedia of Electrochemistry of theElements", Vol XIII, pp 25-33, A. J. Bard Editor, published by MarcelDekker Inc., Advances in Physical Organic Chemistry, vol 20. pp 55-180,V. Gold Editor, 1984, published by Academic Press, N.Y. Also, theelectron donating adsorptive compounds of U.S. Pat. No. 4,607,006 donateonly one electron per molecule upon oxidation. In a preferred embodimentof the present invention, the fragmentable electron donors are capableof donating two electrons.

These fragmentable electron donors of the present invention also differfrom other known photographically active compounds such as R-typingagents, nucleators, and stabilizers. Known R-typing agents, such as Sncomplexes, thiourea dioxide, borohydride, ascorbic acid, and amineboranes are very strong reducing agents. These agents typically undergomulti-electron oxidations but have oxidation potentials more negativethan 0 V vs SCE. For example the oxidation potential for SnCl₂ isreported in CRC Handbook of Chemistry and Physics, 55th edition, CRCPress Inc., Cleveland Ohio 1975, pp D122 to be ˜-0.10 V and that forborohydride is reported in J. Electrochem. Soc., 1992, vol. 139, pp2212-2217 to be -0.48 V vs SCE. These redox characteristics allow for anuncontrolled reduction of silver halide when added to silver halideemulsions, and thus the obtained sensitivity improvements are very oftenaccompanied by undesirable levels of fog. Conventional nucleatorcompounds such as hydrazines and hydrazides differ from the fragmentableelectron donors described herein in that nucleators are usually added tophotographic emulsions in an inactive form. Nucleators are transformedinto photographically active compounds only when activated in a stronglybasic solution, such as a developer solution, wherein the nucleatorcompound undergoes a deprotonation or hydrolysis reaction to afford astrong reducing agent. In further contrast to the fragmentable electrondonors, the oxidation of traditional R-typing agents and nucleatorcompounds is generally accompanied by a deprotonation reaction or ahydroylsis reaction, as opposed to a bond cleavage reaction.

The emulsion layer of the photographic element of the invention cancomprise any one or more of the light sensitive layers of thephotographic element. The photographic elements made in accordance withthe present invention can be black and white elements, single colorelements or multicolor elements. Multicolor elements contain dyeimage-forming units sensitive to each of the three primary regions ofthe spectrum. Each unit can be comprised of a single emulsion layer orof multiple emulsion layers sensitive to a given region of the spectrum.The layers of the element, including the layers of the image-formingunits, can be arranged in various orders as known in the art. In analternative format, the emulsions sensitive to each of the three primaryregions of the spectrum can be disposed as a single segmented layer.

A typical multicolor photographic element comprises a support bearing acyan dye image-forming unit comprised of at least one red-sensitivesilver halide emulsion layer having associated therewith at least onecyan dye-forming coupler, a magenta dye image-forming unit comprising atleast one green-sensitive silver halide emulsion layer having associatedtherewith at least one magenta dye-forming coupler, and a yellow dyeimage-forming unit comprising at least one blue-sensitive silver halideemulsion layer having associated therewith at least one yellowdye-forming coupler. The element can contain additional layers, such asfilter layers, interlayers, overcoat layers, subbing layers, and thelike. All of these can be coated on a support which can be transparentor reflective (for example, a paper support).

Photographic elements of the present invention may also usefully includea magnetic recording material as described in Research Disclosure, Item34390, November 1992, or a transparent magnetic recording layer such asa layer containing magnetic particles on the underside of a transparentsupport as in U.S. Pat. Nos. 4,279,945 and 4,302,523. The elementtypically will have a total thickness (excluding the support) of from 5to 30 microns. While the order of the color sensitive layers can bevaried, they will normally be red-sensitive, green-sensitive andblue-sensitive, in that order on a transparent support, (that is, bluesensitive furthest from the support) and the reverse order on areflective support being typical.

The present invention also contemplates the use of photographic elementsof the present invention in what are often referred to as single usecameras (or "film with lens" units). These cameras are sold with filmpreloaded in them and the entire camera is returned to a processor withthe exposed film remaining inside the camera. Such cameras may haveglass or plastic lenses through which the photographic element isexposed.

In the following discussion of suitable materials for use in elements ofthis invention, reference will be made to Research Disclosure, September1994, Number 365, Item 36544, which will be identified hereafter by theterm "Research Disclosure I." The Sections hereafter referred to areSections of the Research Disclosure I unless otherwise indicated. AllResearch Disclosures referenced are published by Kenneth MasonPublications, Ltd., Dudley Annex, 12a North Street, Emsworth, HampshireP010 7DQ, ENGLAND. The foregoing references and all other referencescited in this application, are incorporated herein by reference.

The silver halide emulsions employed in the photographic elements of thepresent invention may be negative-working, such as surface-sensitiveemulsions or unfogged internal latent image forming emulsions, orpositive working emulsions of internal latent image forming emulsions(that are either fogged in the element or fogged during processing).Suitable emulsions and their preparation as well as methods of chemicaland spectral sensitization are described in Sections I through V. Colormaterials and development modifiers are described in Sections V throughXX. Vehicles which can be used in the photographic elements aredescribed in Section II, and various additives such as brighteners,antifoggants, stabilizers, light absorbing and scattering materials,hardeners, coating aids, plasticizers, lubricants and matting agents aredescribed, for example, in Sections VI through XIII. Manufacturingmethods are described in all of the sections, layer arrangementsparticularly-in Section XI, exposure alternatives in Section XVI, andprocessing methods and agents in Sections XIX and XX.

With negative working silver halide a negative image can be formed.Optionally a positive (or reversal) image can be formed although anegative image is typically first formed.

The photographic elements of the present invention may also use coloredcouplers (e.g. to adjust levels of interlayer correction) and maskingcouplers such as those described in EP 213 490; Japanese PublishedApplication 58-172,647; U.S. Pat. No. 2,983,608; German Application DE2,706,117C; U.K. Patent 1,530,272; Japanese Application A-113935; U.S.Pat. No. 4,070,191 and German Application DE 2,643,965. The maskingcouplers may be shifted or blocked.

The photographic elements may also contain materials that accelerate orotherwise modify the processing steps of bleaching or fixing to improvethe quality of the image. Bleach accelerators described in EP 193 389;EP 301 477; U.S. Pat. No. 4,163,669; U.S. Pat. No. 4,865,956; and U.S.Pat. No. 4,923,784 are particularly useful. Also contemplated is the useof nucleating agents, development accelerators or their precursors (UKPatent 2,097,140; U.K. Patent 2,131,188); development inhibitors andtheir precursors (U.S. Pat. Nos. 5,460,932; U.S. Pat. No. 5,478,711);electron transfer agents (U.S. Pat. Nos. 4,859,578; 4,912,025);antifogging and anti color-mixing agents such as derivatives ofhydroquinones, aminophenols, amines, gallic acid; catechol; ascorbicacid; hydrazides; sulfonamidophenols; and non color-forming couplers.

The elements may also contain filter dye layers comprising colloidalsilver sol or yellow and/or magenta filter dyes and/or antihalation dyes(particularly in an undercoat beneath all light sensitive layers or inthe side of the support opposite that on which all light sensitivelayers are located) either as oil-in-water dispersions, latexdispersions or as solid particle dispersions. Additionally, they may beused with "smearing" couplers (e.g. as described in U.S. Pat. No.4,366,237; EP 096 570; U.S. Pat. Nos. 4,420,556; and 4,543,323.) Also,the couplers may be blocked or coated in protected form as described,for example, in Japanese Application 61/258,249 or U.S. Pat. No.5,019,492.

The photographic elements may further contain other image-modifyingcompounds such as "Development Inhibitor-Releasing" compounds (DIR's).Useful additional DIR's for elements of the present invention, are knownin the art and examples are described in U.S. Pat. Nos. 3,137,578;3,148,022; 3,148,062; 3,227,554; 3,384,657; 3,379,529; 3,615,506;3,617,291; 3,620,746; 3,701,783; 3,733,201; 4,049,455; 4,095,984;4,126,459; 4,149,886; 4,150,228; 4,211,562; 4,248,962; 4,259,437;4,362,878; 4,409,323; 4,477,563; 4,782,012; 4,962,018; 4,500,634;4,579,816; 4,607,004; 4,618,571; 4,678,739; 4,746,600; 4,746,601;4,791,049; 4,857,447; 4,865,959; 4,880,342; 4,886,736; 4,937,179;4,946,767; 4,948,716; 4,952,485; 4,956,269; 4,959,299; 4,966,835;4,985,336 as well as in patent publications GB 1,560,240; GB 2,007,662;GB 2,032,914; GB 2,099,167; DE 2,842,063, DE 2,937,127; DE 3,636,824; DE3,644,416 as well as the following European Patent Publications:272,573; 335,319; 336,411; 346, 899; 362, 870; 365,252; 365,346;373,382; 376,212; 377,463; 378,236; 384,670; 396,486; 401,612; 401,613.

DIR compounds are also disclosed in "Developer-Inhibitor-Releasing (DIR)Couplers for Color Photography," C. R. Barr, J. R. Thirtle and P. W.Vittum in Photographic Science and Engineering, Vol. 13, p. 174 (1969),incorporated herein by reference.

It is also contemplated that the concepts of the present invention maybe employed to obtain reflection color prints as described in ResearchDisclosure, November 1979, Item 18716, available from Kenneth MasonPublications, Ltd, Dudley Annex, 12a North Street, Emsworth, HampshireP0101 7DQ, England, incorporated herein by reference. The emulsions andmaterials to form elements of the present invention, may be coated on pHadjusted support as described in U.S. Pat. No. 4,917,994; with epoxysolvents (EP 0 164 961); with additional stabilizers (as described, forexample, in U.S. Pat. Nos. 4,346,165; 4,540,653 and 4,906,559); withballasted chelating agents such as those in U.S. Pat. No. 4,994,359 toreduce sensitivity to polyvalent cations such as calcium; and with stainreducing compounds such as described in U.S. Pat. Nos. 5,068,171 and5,096,805. Other compounds which may be useful in the elements of theinvention are disclosed in Japanese Published Applications 83-09,959;83-62,586; 90-072,629, 90-072,630; 90-072,632; 90-072,633; 90-072,634;90-077,822; 90-078,229; 90-078,230; 90-079,336; 90-079,338; 90-079,690;90-079,691; 90-080,487; 90-080,489; 90-080,490; 90-080,491; 90-080,492;90-080,494; 90-085,928; 90-086,669; 90-086,670; 90-087,361; 90-087,362;90-087,363; 90-087,364; 90-088,096; 90-088,097; 90-093,662; 90-093,663;90-093,664; 90-093,665; 90-093,666; 90-093,668; 90-094,055; 90-094,056;90-101,937; 90-103,409; 90-151,577.

The silver halide used in the photographic elements may be silveriodobromide, silver bromide, silver chloride, silver chlorobromide,silver chloroiodobromide, and the like.

The type of silver halide grains preferably include polymorphic, cubic,and octahedral. The grain size of the silver halide may have anydistribution known to be useful in photographic compositions, and may beeither polydipersed or monodispersed.

Tabular grain silver halide emulsions may also be used. Tabular grainsare those with two parallel major faces each clearly larger than anyremaining grain face and tabular grain emulsions are those in which thetabular grains account for at least 30 percent, more typically at least50 percent, preferably >70 percent and optimally >90 percent of totalgrain projected area. The tabular grains can account for substantiallyall (>97 percent) of total grain projected area. The tabular grainemulsions can be high aspect ratio tabular grain emulsions--i.e.,ECD/t>8, where ECD is the diameter of a circle having an area equal tograin projected area and t is tabular grain thickness; intermediateaspect ratio tabular grain emulsions--i.e., ECD/t=5 to 8; or low aspectratio tabular grain emulsions--i.e., ECD/t=2 to 5. The emulsionstypically exhibit high tabularity (T), where T (i.e., ECD/t²)>25 and ECDand t are both measured in micrometers (μm). The tabular grains can beof any thickness compatible with achieving an aim average aspect ratioand/or average tabularity of the tabular grain emulsion. Preferably thetabular grains satisfying projected area requirements are those havingthicknesses of <0.3 μm. thin (<0.2 μm) tabular grains being specificallypreferred and ultrathin (<0.07 μm) tabular grains being contemplated formaximum tabular grain performance enhancements. When the native blueabsorption of iodohalide tabular grains is relied upon for blue speed,thicker tabular grains, typically up to 0.5 μm in thickness, arecontemplated.

High iodide tabular grain emulsions are illustrated by House U.S. Pat.No. 4,490,458, Maskasky U.S. Pat. No. 4,459,353 and Yagi et al EPO 0 410410.

Tabular grains formed of silver halide(s) that form a face centeredcubic (rock salt type) crystal lattice structure can have either {100}or {111} major faces. Emulsions containing {111} major face tabulargrains, including those with controlled grain dispersities, halidedistributions, twin plane spacing, edge structures and graindislocations as well as adsorbed {111} grain face stabilizers, areillustrated in those references cited in Research Disclosure I, SectionI.B.(3) (page 503).

The silver halide grains to be used in the invention may be preparedaccording to methods known in the art, such as those described inResearch Disclosure I and James, The Theory of the Photographic Process.These include methods such as ammoniacal emulsion making, neutral oracidic emulsion making, and others known in the art. These methodsgenerally involve mixing a water soluble silver salt with a watersoluble halide salt in the presence of a protective colloid, andcontrolling the temperature, pAg, pH values, etc, at suitable valuesduring formation of the silver halide by precipitation.

In the course of grain precipitation one or more dopants (grainocclusions other than silver and halide) can be introduced to modifygrain properties. For example, any of the various conventional dopantsdisclosed in Research Disclosure, Item 36544, Section I. Emulsion grainsand their preparation, sub-section G. Grain modifying conditions andadjustments, paragraphs (3), (4) and (5), can be present in theemulsions of the invention. In addition it is specifically contemplatedto dope the grains with transition metal hexacoordination complexescontaining one or more organic ligands, as taught by Olm et al U.S. Pat.No. 5,360,712, the disclosure of which is here incorporated byreference.

It is specifically contemplated to incorporate in the face centeredcubic crystal lattice of the grains a dopant capable of increasingimaging speed by forming a shallow electron trap (hereinafter alsoreferred to as a SET) as discussed in Research Discolosure Item 36736published November 1994, here incorporated by reference.

The SET dopants are effective at any location within the grains.Generally better results are obtained when the SET dopant isincorporated in the exterior 50 percent of the grain, based on silver.An optimum grain region for SET incorporation is that formed by silverranging from 50 to 85 percent of total silver forming the grains. TheSET can be introduced all at once or run into the reaction vessel over aperiod of time while grain precipitation is continuing. Generally SETforming dopants are contemplated to be incorporated in concentrations ofat least 1×10⁻⁷ mole per silver mole up to their solubility limit,typically up to about 5×10⁻⁴ mole per silver mole.

SET dopants are known to be effective to reduce reciprocity failure. Inparticular the use of iridium hexacoordination complexes or Ir⁺⁴complexes as SET dopants is advantageous.

Iridium dopants that are ineffective to provide shallow electron traps(non-SET dopants) can also be incorporated into the grains of the silverhalide grain emulsions to reduce reciprocity failure.

To be effective for reciprocity improvement the Ir can be present at anylocation within the grain structure. A preferred location within thegrain structure for Ir dopants to produce reciprocity improvement is inthe region of the grains formed after the first 60 percent and beforethe final 1 percent (most preferably before the final 3 percent) oftotal silver forming the grains has been precipitated. The dopant can beintroduced all at once or run into the reaction vessel over a period oftime while grain precipitation is continuing. Generally reciprocityimproving non-SET Ir dopants are contemplated to be incorporated attheir lowest effective concentrations.

The contrast of the photographic element of can be further increased bydoping the grains with a hexacoordination complex containing a nitrosylor thionitrosyl ligand (NZ dopants) as disclosed in McDugle et al U.S.Pat. No. 4,933,272, the disclosure of which is here incorporated byreference.

The contrast increasing dopants can be incorporated in the grainstructure at any convenient location. However, if the NZ dopant ispresent at the surface of the grain, it can reduce the sensitivity ofthe grains. It is therefore preferred that the NZ dopants be located inthe grain so that they are separated from the grain surface by at least1 percent (most preferably at least 3 percent) of the total silverprecipitated in forming the silver iodochloride grains. Preferredcontrast enhancing concentrations of the NZ dopants range from 1×10⁻¹¹to 4×10⁻⁸ mole per silver mole, with specifically preferredconcentrations being in the range from 10⁻¹⁰ to 10⁻⁸ mole per silvermole.

Although generally preferred concentration ranges for the various SET,non-SET Ir and NZ dopants have been set out above, it is recognized thatspecific optimum concentration ranges within these general ranges can beidentified for specific applications by routine testing. It isspecifically contemplated to employ the SET, non-SET Ir and NZ dopantssingly or in combination. For example, grains containing a combinationof an SET dopant and a non-SET Ir dopant are specifically contemplated.Similarly SET and NZ dopants can be employed in combination. Also NZ andIr dopants that are not SET dopants can be employed in combination.Finally, the combination of a non-SET Ir dopant with a SET dopant and anNZ dopant. For this latter three-way combination of dopants it isgenerally most convenient in terms of precipitation to incorporate theNZ dopant first, followed by the SET dopant, with the non-SET Ir dopantincorporated last.

The photographic elements of the present invention, as is typical,provide the silver halide in the form of an emulsion. Photographicemulsions generally include a vehicle for coating the emulsion as alayer of a photographic element. Useful vehicles include both naturallyoccurring substances such as proteins, protein derivatives, cellulosederivatives (e.g., cellulose esters), gelatin (e.g., alkali-treatedgelatin such as cattle bone or hide gelatin, or acid treated gelatinsuch as pigskin gelatin), gelatin derivatives (e.g., acetylated gelatin,phthalated gelatin, and the like), and others as described in ResearchDisclosure I. Also useful as vehicles or vehicle extenders arehydrophilic water-permeable colloids. These include synthetic polymericpeptizers, carriers, and/or binders such as poly(vinyl alcohol),poly(vinyl lactams), acrylamide polymers, polyvinyl acetals, polymers ofalkyl and sulfoalkyl acrylates and methacrylates, hydrolyzed polyvinylacetates, polyamides, polyvinyl pyridine, methacrylamide copolymers, andthe like, as described in Research Disclosure I. The vehicle can bepresent in the emulsion in any amount useful in photographic emulsions.The emulsion can also include any of the addenda known to be useful inphotographic emulsions.

The silver halide to be used in the invention may be advantageouslysubjected to chemical sensitization. Compounds and techniques useful forchemical sensitization of silver halide are known in the art anddescribed in Research Disclosure I and the references cited therein.Compounds useful as chemical sensitizers, include, for example, activegelatin, sulfur, selenium, tellurium, gold, platinum, palladium,iridium, osmium, rhenium, phosphorous, or combinations thereof. Chemicalsensitization is generally carried out at pAg levels of from 5 to 10, pHlevels of from 4 to 8, and temperatures of from 30 to 80° C., asdescribed in Research Disclosure I, Section IV (pages 510-511) and thereferences cited therein.

The silver halide may be sensitized by sensitizing dyes by any methodknown in the art, such as described in Research Disclosure I. The dyemay be added to an emulsion of the silver halide grains and ahydrophilic colloid at any time prior to (e.g., during or after chemicalsensitization) or simultaneous with the coating of the emulsion on aphotographic element. The dyes may, for example, be added as a solutionin water or an alcohol. The dye/silver halide emulsion may be mixed witha dispersion of color image-forming coupler immediately before coatingor in advance of coating (for example, 2 hours).

Photographic elements of the present invention are preferably imagewiseexposed using any of the known techniques, including those described inResearch Disclosure I, section XVI. This typically involves exposure tolight in the visible region of the spectrum, and typically such exposureis of a live image through a lens, although exposure can also beexposure to a stored image (such as a computer stored image) by means oflight emitting devices (such as light emitting diodes, CRT and thelike).

Photographic elements comprising the composition of the invention can beprocessed in any of a number of well-known photographic processesutilizing any of a number of well-known processing compositions,described, for example, in Research Disclosure I, or in T. H. James,editor, The Theory of the Photographic Process, 4th Edition, Macmillan,New York, 1977. In the case of processing a negative working element,the element is treated with a color developer (that is one which willform the colored image dyes with the color couplers), and then with aoxidizer and a solvent to remove silver and silver halide. In the caseof processing a reversal color element, the element is first treatedwith a black and white developer (that is, a developer which does notform colored dyes with the coupler compounds) followed by a treatment tofog silver halide (usually chemical fogging or light fogging), followedby treatment with a color developer. Preferred color developing agentsare p-phenylenediamines. Especially preferred are: 4-aminoN,N-diethylaniline hydrochloride, 4-amino-3-methyl-N,N-diethylanilinehydrochloride, 4-amino-3-methyl-N-ethyl-N-(β-(methanesulfonamido)ethylaniline sesquisulfate hydrate,4-amino-3-methyl-N-ethyl-N-(β-hydroxyethyl)aniline sulfate,4-amino-3-β-(methanesulfonamido)ethyl-N,N-diethylaniline hydrochlorideand 4-amino-N-ethyl-N-(2-methoxyethyl)-m-toluidine di-p-toluene sulfonicacid.

Dye images can be formed or amplified by processes which employ incombination with a dye-image-generating reducing agent an inerttransition metal-ion complex oxidizing agent, as illustrated byBissonette U.S. Pat. Nos. 3,748,138, 3,826,652, 3,862,842 and 3,989,526and Travis U.S. Pat. No. 3,765,891, and/or a peroxide oxidizing agent asillustrated by Matejec U.S. Pat. No. 3,674,490, Research Disclosure,Vol. 116, December, 1973, Item 11660, and Bissonette ResearchDisclosure, Vol. 148, August, 1976, Items 14836, 14846 and 14847. Thephotographic elements can be particularly adapted to form dye images bysuch processes as illustrated by Dunn et al U.S. Pat. No. 3,822,129,Bissonette U.S. Pat. Nos. 3,834,907 and 3,902,905, Bissonette et al U.S.Pat. No. 3,847,619, Mowrey U.S. Pat. No. 3,904,413, Hirai et al U.S.Pat. No. 4,880,725, Iwano U.S. Pat. No. 4,954,425, Marsden et al U.S.Pat. No. 4,983,504, Evans et al U.S. Pat. No. 5,246,822, Twist U.S. Pat.No. No. 5,324,624, Fyson EPO 0 487 616, Tannahill et al WO 90/13059,Marsden et al WO 90/13061, Grimsey et al WO 91/16666, Fyson WO 91/17479,Marsden et al WO 92/01972. Tannahill WO 92/05471, Henson WO 92/07299,Twist WO 93/01524 and WO 93/11460 and Wingender et al German OLS4,211,460.

Development is followed by bleachfixing, to remove silver or silverhalide, washing and drying.

The fragmentable electron donating sensitizer compounds of the presentinvention can be included in a silver halide emulsion by directdispersion in the emulsion, or they may be dissolved in a solvent suchas water, methanol or ethanol for example, or in a mixture of suchsolvents, and the resulting solution can be added to the emulsion. Thecompounds of the present invention may also be added from solutionscontaining a base and/or surfactants, or may be incorporated intoaqueous slurries or gelatin dispersions and then added to the emulsion.The compounds are generally used together with conventional sensitizingdye, and can be added before, during or after the addition of theconventional sensitizing dye.

The amount of fragmentable electron donating compound which is employedin this invention may range from as little as 1×10⁻⁸ to as much as about2×10⁻³ mole per mole of silver in an emulsion layer. More preferably theconcentration of the compounds is from about 5×10⁻⁷ to about 2×10⁻⁴ moleper mole of silver in an emulsion layer. Where the oxidation potentialE₁ for the XY group of the fragmentable two-electron donating sensitizeris a relatively low potential, it is more active, and relatively lessagent need be employed. Conversely, where the oxidation potential forthe XY group of the fragmentable two-electron donating sensitizer isrelatively high, a larger amount thereof, per mole of silver, isemployed. For fragmentable one-electron donating sensitizers relativelylarger amounts per mole of silver are also employed.

Conventional spectral sensitizing dyes can be used in combination withthe fragmentable electron donating spectral sensitizing agent of thepresent invention, including cyanine dyes, complex cyanine dyes,merocyanine dyes, complex merocyanine dyes, styryl dyes, oxonol dyes,hemioxonol dyes, and hemicyanine dyes. Preferrably the conventionalspectral sensitizing dye is a compound of the formulae VIII-XII setforth above. The ratio of conventional spectral sensitizing dye to thefragmentable electron donating sensitizing agent of the presentinvention, which may be determined through an ordinary emulsion test, istypically from about 99.95:0.05 to about 90:10 by mol.

Various compounds may be added to the photographic material of thepresent invention for the purpose of lowering the fogging of thematerial during manufacture, storage, or processing. Typicalantifoggants are discussed in Section VI of Research Disclosure I, forexample tetraazaindenes, mercaptotetrazoles, polyhydroxybenzenes,hydroxyaminobenzenes, combinations of a thiosulfonate and a sulfinate,and the like.

For this invention, polyhydroxybenzene and hydroxyaminobenzene compounds(hereinafter "hydroxybenzene compounds") are preferred as they areeffective for lowering fog without decreasing the emulsion sensitvity.Examples of hydroxybenzene compounds are: ##STR61##

In these formulae, V and V' each independently represent --H, --OH, ahalogen atom, --OM (M is alkali metal ion), an alkyl group, a phenylgroup, an amino group, a carbonyl group, a sulfone group, a sulfonatedphenyl group, a sulfonated alkyl group, a sulfonated amino group, acarboxyphenyl group, a carboxyalkyl group, a carboxyamino group, ahydroxyphenyl group, a hydroxyalkyl group, an alkylether group, analkylphenyl group, an alkylthioether group, or a phenylthioether group.

More preferably, they each independently represent --H, --OH, --Cl,--Br, --COOH, --CH₂ CH₂ COOH, --CH₃, --CH₂ CH₃, --C(CH₃)₃, --OCH₃,--CHO, --SO₃ K,--SO₃ Na, --SO₃ H,

SCH₃, or --phenyl.

Especially preferred hydroxybenzene compounds follow: ##STR62##

Hydroxybenzene compounds may be added to the emulsion layers or anyother layer constituting the photographic material of the presentinvention. The preferred amount added is from 1×10⁻³ to 1×10⁻¹ mol, andmore preferred is 1×10⁻³ to 2×10⁻² mol, per mol of silver halide.

Laser Flash Photolysis Method

(a) Oxidation Potential of Radical X.sup.•

The laser flash photolysis measurements were performed using ananosecond pulsed excimer (Questek model 2620, 308 nm, ca. 20 ns, ca.100 mJ) pumped dye laser (Lambda Physik model FL 3002). The laser dyewas DPS (commercially available from Exciton Co.) in p-dioxane (410 nm,ca. 20 ns, ca. 10 mJ). The analyzing light source was a pulsed 150Wxenon arc lamp (Osram XBO 150/W). The arc lamp power supply was a PRAmodel 302 and the pulser was a PRA model M-306. The pulser increased thelight output by ca. 100 fold, for a time period of ca. 2-3 ms. Theanalyzing light was focussed through a small aperture (ca. 1.5 mm) in acell holder designed to hold 1 cm² cuvettes. The laser and analyzingbeams irradiated the cell from opposite directions and crossed at anarrow angle (ca. 15°). After leaving the cell, the analyzing light wascollimated and focussed onto the slit (1 mm, 4 nm bandpass) of an ISAH-20 monochromator. The light was detected using 5 dynodes of aHamamatsu model R446 photomultiplier. The output of the photomultipliertube was terminated into 50 ohm, and captured using a Tektronix DSA-602digital oscilloscope. The entire experiment is controlled from apersonal computer.

The experiments were performed either in acetonitrile, or a mixture of80% acetonitrile and 20% water. The first singlet excited state of acyanoanthracene (A), which acted as the electron acceptor, was producedusing the nanosecond laser pulse at 410 nm. Quenching of this excitedstate by electron transfer from the relatively high oxidation potentialdonor biphenyl (B), resulted in efficient formation of separated,"free", radical ions in solution, A.sup.•- +B.sup.•+. Secondary electrontransfer then occurred between B.sup.•+ and the lower oxidationpotential electron donor X-Y, to generate X-Y.sup.•+ in high yield. Forthe investigations of the oxidation potentials of the radicals X.sup.•,typically the cyanoanthrancene concentration was ca. 2×10⁻⁵ M to 10⁻⁴ M,the biphenyl concentration was ca. 0.1 M. The concentration of the X-Ydonor was ca. 10⁻³ M. The rates of the electron transfer reactions aredetermined by the concentrations of the substrates. The concentrationsused ensured that the A.sup.•- and the X-Y.sup.•+ were generated within100 ns of the laser pulse. The radical ions could be observed directlyby means of their visible absorption spectra. The kinetics of thephotogenerated radical ions were monitored by observation of the changesin optical density at the appropriate wavelengths.

The reduction potential (E_(red)) of 9,10-dicyanoanthracene (DCA) is-0.91 V. In a typical experiment, DCA is excited and the initialphotoinduced electron transfer from the biphenyl (B) to the DCA forms aDCA.sup.•-, which is observed at its characteristic absorption maximum(λ_(obs) =705 nm), within ca. 20 ns of the laser pulse. Rapid secondaryelectron transfer occurs from X-Y to B.sup.•+ to generate X-Y.sup.•+,which fragments to give X.sup.•. A growth in absorption is then observedat 705 nm with a time constant of ca. 1 microsecond, due to reduction ofa second DCA by the X.sup.•. The absorption signal with the microsecondgrowth time is equal to the size of the absorption signal formed within20 ns. If reduction of two DCA was observed in such an experiment, thisindicates that the oxidation potential of the X.sup.• is more negativethan -0.9 V.

If the oxidation potential of X.sup.• is not sufficiently negative toreduce DCA, an estimate of its oxidation potential was obtained by usingother cyanoanthracenes as acceptors. Experiments were performed in anidentical manner to that described above except that2,9,10-tricyanoanthracene (TriCA, E_(red) -0.67 V, λ_(obs) =710 nm) ortetracyanoanthracene (TCA, E_(red) -0.44 V, λ_(obs) =715 nm) were usedas the electron acceptors. The oxidation potential of the X.sup.• wastaken to be more negative than -0.7 if reduction of two TriCA wasobserved, and more negative than -0.5 V if reduction of two TCA wasobserved. Occasionally the size of the signal from the second reducedacceptor was smaller than that of the first. This was taken to indicatethat electron transfer from the X.sup.• to the acceptor was barelyexothermic, i.e. the oxidation potential of the radical was essentiallythe same as the reduction potential of the acceptor.

To estimate the oxidation potentials of X.sup.• with values lessnegative than -0.5 V, i.e. not low enough to reduce eventetracyanoanthracene, a slightly different approach was used. In thepresence of low concentrations of an additional acceptor, Q, that has aless negative reduction potential than the primary acceptor, A (DCA, forexample), secondary electron transfer from A.sup.•- to Q will takeplace. If the reduction potential of Q is also less negative than theoxidation potential of the X.sup.•, then Q will also be reduced by theradical, and the magnitude of the Q.sup.•- absorption signal will bedoubled. In this case, both the first and the second electron transferreactions are diffusion controlled and occur at the same rate.Consequently, the second reduction cannot be time resolved from thefirst. Therefore, to determine whether two electron reduction actuallytakes place, the Q.sup.•- signal size must be compared with an analogoussystem for which it is known that reduction of only a single Q occurs.For example, a reactive X-Y.sup.•+ which might give a reducing X.sup.•can be compared with a nonreactive X-Y.sup.•+. Useful secondary electronacceptors (Q) that have been used are chlorobenzoquinone (E_(red) -0.34V, λ_(obs) =450 nm), 2,5-dichlorobenzoquinone (E_(red) -0.18 V, λ_(obs)=455 nm) and 2,3,5,6-tetrachlorobenzoquinone (E_(red) 0.00 V, λ_(obs)=460 nm). (b) Fragmentation Rate Constant Determination

The laser flash photolysis technique was also used to determinefragmentation rate constants for examples of the oxidized donors X-Y.The radical cations of the X-Y donors absorb in the visible region ofthe spectrum. Spectra of related compounds can be found in "ElectronAbsorption Spectra of Radical Ions" by T. Shida, Elsevier, New York,1988. These absorptions were used to determine the kinetics of thefragmentation reactions of the radical cations of the X-Y. Excitation of9,10-dicyanoanthracene (DCA) in the presence of biphenyl and the X-Ydonor, as described above, results in the formation of the DCA.sup.•-and the X-Y.sup.•+. By using a concentration of X-Y of ca. 10⁻² M, theX-Y.sup.•+ can be formed within ca. 20 ns of the laser pulse. With themonitoring wavelength set within an absorption band of the X-Y.sup.•+, adecay in absorbance as a function of time is observed due to thefragmentation reaction. The monitoring wavelengths used were somewhatdifferent for the different donors, but were mostly around 470-530 nm.In general the DCA.sup.•- also absorbed at the monitoring wavelengths,however, the signal due to the radical anion was generally much weakerthan that due to the radical cation, and on the timescale of theexperiment the A.sup.•- did not decay, and so did not contribute to theobserved kinetics. As the X-Y.sup.•+ decayed, the radical X.sup.• wasformed, which in most cases reacted with the cyanoanthracene to form asecond A.sup.•-. To make sure that this "grow-in" of absorbance due toA.sup.•- did not interfere with the time-resolved decay measurements,the concentration of the cyanoanthracene was maintained below ca. 2×10⁻⁵M. At this concentration the second reduction reaction occurred on amuch slower timescale than the X-Y.sup.•+ decay. Alternatively, when thedecay rate of the X-Y.sup.•+ was less than 10⁶ s⁻¹, the solutions werepurged with oxygen. Under these conditions the DCA.sup.•- reacted withthe oxygen to form O₂.sup.•- within 100 ns, so that its absorbance didnot interfere with that of the X-Y.sup.•+ on the timescale of its decay.

The experiments measuring the fragmentation rate constants wereperformed in acetonitrile with the addition of 20% water, so that all ofthe salts could be easily solubilized. Most experiments were performedat room temperature. In some cases the fragmentation rate was either toofast or too slow to be easily determined at room temperature. When thishappened, the fragmentation rate constants were measured as a functionof temperature, and the rate constant at room temperature determined byextrapolation.

Typical examples of synthesis of compounds Z-L-XY follow. Othercompounds can also be synthesized by analogy using appropriate selectedknown starting materials. The following compounds are synthesized byreaction Scheme I, II and III. ##STR63## wherein R₄₆ is CH₂ CH₃ or(CH₂)₃ SO₃ --. Preparation Intermediate (c)

To 21 g of p-toluidine in 25 ml of toluene was added 1 equiv of t-butylacrylate. The mixture was allowed to react for 40 hr at reflux and themonoalkylated product was isolated by vacuum distillation to give 33 g(70%) of (a), b.p. 120-150° C./1-2.5 mm. To 116 g of (a) in 600 ml ofbutyronitrile was added 2 equiv. of K₂ CO₃ and 2 equiv ofethyl-2-bromoproprionate and the mixture was heated to reflux and heldfor 16 h., from which 116 g (60%) of compound (b) was isolated bydistillation, b.p. 145-170° C./0.5-0.7 mm. To 5.36 g of the t-butylester compound (b) was added 6 ml of trifluoroacetic acid (TFA) and theresulting solution was kept over night at room temperature. Excess TFAwas removed to give 5 g of compound (c) as the residue. ¹ H-NMR, andfield desorption mass-spectrometric (FDMS) measurements were consistentwith the proposed structure. Analysis Results: FDMS; m/e 279 (M⁺) forC₁₅ H₂₁ NO₄ ; ¹ H-NMR (CDCl₃): δ 1.22 (t, 3H), 1.49 (d, 3H), 2.36 (s,3H), 2.55 (m, 2H), 3.86 (t, 2H), 4.19 (q, 2H), 4.40 (q, 1H), 7.28 (m,4H), 9.29 (s, 1H). Compounds analogous to intermediate (c) can besynthesized by using appropriate p-substituted anilines as a startingmaterial.

Preparation of Aminoalkylsubstituted Cyanine Dye Intermediate (g)

A mixture of N-(4-bromobutyl) phathalimide (5.64 g, 0.02 mole) and5-chloro-2-methylbenzothiazole (3.86 g, 0.002 mole) was taken in asealed tube and heated in an oil bath at 150-160° C. under magneticstirring for 20 hr. The residue was triturated with ethyl acetate. Thelight brown solid material (d) was collected on a sintered glass funnel,washed thoroughly with ethyl acetate and air-dried. Yield of (d) was 4.7g (50.05%). Other quarternary salts were prepared in the same way. Thequaternary salt (0.01 mole) and an oxime of general formula (e) (0.01mole) were mechanically stirred in acetonitrile (400 mL) at roomtemperature. Distilled water (140 mL) was added slowly to make thereaction mixture a homogeneous solution. Acetic anhydride (3.0 mL) wasadded, and the mixture was stirred for 5 min. Then triethylamine (8.0mL) was added, and the reaction mixture changed to a light brownhomogeneous solution. The phthalimidocyanine dye (f) started toprecipitate after 15-20 min. The reaction mixture was stirred foranother 2.5 hr. The gelatinous dark yellow precipitate of (f) wascollected on a sintered glass funnel, thoroughly washed with acetone,air-dried, and purified by flash column chromatography. Thephthalimidocyanine dye (f) (0.00186 mole), 50 mL of 31% HBr/acetic acid,and 20 mL of 49% HBr/H₂ O were placed together with a magnetic stirringbar in a reaction tube. Trifluoroacetic acid (TFA, 15 mL) was slowlyadded and the reaction mixture was heated in an oil bath at 140° C. withstirring for 48-60 hr., then allowed to cool to 30-35° C. The solventwas removed on a rotary evaporator under vacuum. The thick yellowresidue was diluted with 150 mL of reagent grade acetone and agitatedwith a glass rod. The resulting solid, intermediate (g), was collectedon a sintered glass funnel, washed successively with acetone (2×100 mL)and ether (2×100 mL), and air-dried for 2-3 hr. The product (g) waspurified by column chromatography or recrystallization.

Preparation of Comp 6

A mixture of 1.3 g (2.2 mmol) of Dye (g) (g, R₄₆ =Et), 1.07 g (4equivalents) of 4-N,N-dimethylaminopyridine and 540 mg (2 equiv) of1,5-diazobicyclo[4.3.0]non-5-ene (DBN) in 40 mL of dimethylsulfoxide(dried in 3A molecular sieve prior to use) was sonicated until asolution was obtained. To this solution was added 1 g (3.6 mmol) of thecrude compound (c) followed by 1 g (2 equiv) of2-chloro-N-methylpyridinium triflate and the reaction mixture wasallowed to stir overnight at room temperature. Addition of 200 mL ofwater precipitated a yellow dye which was filtered, washed thoroughlywith water and dried in air to give about 3.18 g of the crude Comp 6.This material was saponified without further purification.FAB Mass: m/e697 (M⁺ for C₃₅ H₂₃ Cl₂ N₄ O₃ S₂ ⁺) and 149 (M⁻ for CF₃ SO₃ ⁻);Characteristic peaks of ¹ H-NMR (DMSO-d₆): d 0.99 (t J=7 Hz, 3H), 1.21(d J=7 Hz, 3H), 1.99 (s, 3H), 6.41 (d J=8.4 Hz, 2H), 6.50 (s, 1H), 6.75(d J=8.3 Hz, 2H), 7.39 (d J=8.5 Hz, 2H), 7.80 (s, 1H), 7.86 (s, 1H),7.97 (d J=4.5 Hz, 2H), 8.0 (d J=4.3 Hz, 2H), 8.02 (s, 1H)

Preparation of Inv 13

1.57 g of the crude Comp 6 was saponified with 75 mL of 1N NaOH in 125mL of methanol at room temperature for 2 h. Excess methanol was removedon a rotary evaporator at about 30° C. until solid started to appear. Tothe residue was added 200 mL of water and some brine. The precipitateddye was filtered and washed thoroughly with water, dried in vacuum togive 0.47 g of the crude product. This product was purified by washingwith chloroform and the insoluble solid was recrystallized from ethanolto give 140 mg of pure Inv 13. ¹ H-NMR, and mass spectrometricmeasurements were consistent with the proposed structure. FAB massspectrum: m/e 669 (MH⁺ for C₃₃ H₁₉ Cl₂ N₄ O₃ S₂ ⁺)

Synthesis Example 2

The compound Comp 2 and Inv 11 were prepared as in synthesis example 1,scheme I, using the dye intermediate (g) where R₄₆ is a 3-sulfopropylgroup.

Preparation of Comp 2

A mixture of 2.1 g (3.46 mmol) of intermediate (g) where R₄₆ is a3-sulfopropyl group, 1.3 g (3 equiv) of 4-(dimethylamino)pyridine and540 mg (2 equiv) of DBN in 40 mL of dimethylsulfoxide (dried in 3Amolecular sieve prior to use) was sonicated and then added to thismixture was 1.46 g (5.2 mmol) of the crude compound (c) and 1.67 g (2equiv) of 2-chloro-N-methylpyridinium triflate. After allowing themixture to react for 12 h at room temperature, 300 mL of water was addedto give a yellow precipitate, which was filtered, washed thoroughly withwater and dried in air to give about 2.15 g of the crude product.Purification was achieved by recrystallization from ethanol to give 2 gof yellow Comp 2. FAB Mass: m/e 805 (M⁺ for C₃₇ H₂₆ Cl₂ N₄ O₆ S₃ ^(+'))and 804 (M⁻ for C₃₇ H₂₅ Cl₂ N₄ O₆ S₃ ⁻); Characteristic peaks of ¹ H-NMR(CDCl₃) are: δ 1.12 (t J=7.1 Hz, 3H), 1.23 (t J=7 Hz, 3H) 1.43 (d J=7.1Hz, 3H), 2.11 (s, 3H), 3.71 (q J=7 Hz, 2H), 3.97 (q J=7.1 Hz, 2H), 6.58(d J=8.1 Hz, 2H), 6.87 (d J=8.3 Hz, 2H), 7.35 (s, 1H), 7.40 (d J=9.7 Hz,2H), 7.43 (d J=12.5 Hz, 2H), 7.52 (s, 1H), 7.72 (d J=9 Hz, 2H), 7.75 (dJ=9 Hz, 2H), 7.84 (broad t , 1H, NH). The protons in aromatic region arebetter characterized by ¹ H-NMR in DMSO-d₆ : d 6.34 (d J=8.3 Hz, 2H),6.61 (d J=8.2 Hz, 2H), 6.77 (s, 1H), 7.23 (d J=8.4 Hz, 1H), 7.32 (dJ=8.9 Hz, 1H), 7.74 (s, 1H), 7.80 (s, 1H), 7.84 (d J=8.5 Hz, 1H), 7.92(d J=8.5 Hz, 1H), 8.0 (broad t, 1H, NH).

Preparation of Inv 11

Comp 2 (600 mg) was saponified with 32 mL of 0.25N NaOH in 80 mL ofmethanol at room temperature. The reaction was carefully monitored byHPLC analysis until all the dye ester was hydrolyzed. Excess NaOH wasneutralized with 5N HCl added dropwise until the final pH was about 7-8.Most of the methanol was removed on a rotary evaporator at about 30°-35°C. until solid started to appear. The crude product was filtered andwashed with brine and dried giving a total of 630 mg of yellow material.This was dissolved in 10-15 mL of methanol containing acetonitrile andmethanol to yield 130 mg of the pure Inv 11. Analysis Results: FAB massspectrum: m/e 777 (MH₂ ⁺ for C₃₅ H₂₁ Cl₂ N₄ O₆ S₃ +2H⁺), 799 (MH⁺ Na⁺for C₃₅ H₂₁ Cl₂ N₄ O₆ S₃ +H⁺ +Na⁺); Characteristic peaks of ¹ H-NMR (CD₃OD) are: d 1.26 (d J=7.4 Hz, 3H), 3.49 (q J=6.1 Hz, 2H), 4.01 (q J=7.1Hz, 1H), 6.53 (d J=7.6 Hz, 2H), 6.70 (d J=8.1 Hz, 2H), 6.90 (s, 1H), 7.3(d,d J=8.3; 1.6 Hz, 1H) 7.39 (d,d J=8.2; 1.2 Hz, 1H), 7.68 (d, J=1.1 Hz,1H), 7.78 (broad s, 1H), 7.81 (d J=8.5 Hz, 1H), 7.91 (d J=8.5 Hz, 1H).

Synthesis Example 3

The compound Comp 5 and Inv 15 were prepared as in synthesis example 1using ethyl p-aminophenylacetate as a starting material and using ethyliodide in place of ethyl-2-bromoproprionate for the preparation ofintermediate (b), and using dye intermediate (g) where R₄₆ is an ethylgroup. This synthesis is outlined in Scheme II. ##STR64## Preparation ofComp 5 (Scheme II)

A solution of 5 g (27.9 mmol) of ethyl p-aminophenylacetate in 20 mL ofacetic acid was added 4.9 mL of t-butyl acrylate. The mixture was heatedin an oil bath of 110-5° C. for 3-4 h. It was poured into water,extracted with ether, dried by the addition of MgSO₄, and rotavaporatedto give 7.5 g of crude intermediate (j). A mixture of 3.8 g ofintermediate (i), 3 mL of ethyl iodide, and 2.5 g of anhydrous K₂ CO₃ in50 mL of acetonitrile was refluxed for 15 h. It was then poured intowater and extracted with ether. The organic phase was separated, dried(MgSO₄) and rotavaporated to give 2.4 g of a dark oil. Purification wasaccomplished by dissolving in methylene chloride and passing through a1"×3" column of silica gel (32-63 micron). The eluent was rotavaporatedto give 21.5 g of pure intermediate (k) as a colorless oil. 5 mL oftrifluroracetic acid TFA was added to the oil and the solution was keptat room temperature overnight. Excess TFA was rotavaporated and theresidue was dried under high vacuum (0.1 mm) to give 2.7 g ofintermediate (1).

A mixture of 650 mg (0.5 eq) of Dye (g) where R₄₆ =ethyl, 390 mg ofDMAP, 265 mg of DEN, and 300 mg of intermediate (1) in 30 mL of DMSO wasstirred until a solution was obtained. To this was added 390 mg (1.5equiv) of 2-chloro-N-methylpyridinium triflate and the reaction mixturewas allowed to stir overnight at room temperature. The mixuture waspoured into 150 mL of water and 1000 mL of brine which precipitated afinely suspended solid. The emulsion-like mixture was allowed to standovernight to allow the solid to coaggulate and settle down at the bottomof the beaker. It was then filtered readily and evaporated to dryness.Purification was accomplished by flash chromatography over a 1"×5"silica gel (32-63 m) column packed in methylene chloride/isopropanol(7/1 v/v) to give 200 mg of pure Comp 5. FAB mass spectrum: m/e 711 (M⁺for C₃₆ H₄₁ Cl₂ N₄ O₃ S₂ ⁺) and m/e 149 (M⁻ for CF₃ SO₃ ⁻);characteristic peaks of ¹ H-NMR(DMSO-d₆): d 0.96 (t J=7 Hz, 3H), 1.14 (tJ=7.1 Hz, 3H, 1.34 (t J=7 Hz, 3H),1.61 (t, 2H), 1.73 (m, 4H), 1.94 (m,1H), 2.06 (m, 1H), 3.23 (m, 4H), 3.34 (s, 2H), 3.48 (t J=7 Hz, 2H), 3.99(q J=7 Hz, 2H), 4.42 (q, 1H), 4.43 (t J=6.5 Hz, 2H), 4.49 (q J=7.2 Hz,2H) 6.56 (d, 2H), 6.66 (s, 1H), 7.29 (d, 1H), 7.23 (t, 1H), 7.31 (s,1H), 7.40 (s, 1H), 7.73 (d J=8.2 Hz, 1H), 7.75 (d J=8.2 Hz, 1H).

Preparation of Inv 15

Comp 5 (450 mg) was saponified with 10 mL of 0.25N NaOH in 20 mL ofmethanol at room temperature for 3 h. The precipitated yellow solid wasremoved by filtration and washed with a little water, and then dried togive 70 mg of the Inv 15: FAB mass spectra: m/e 783 (MH⁺ for C₃₄ H₃₆ Cl₂N₄ O₃ S+H⁺); characteristic peaks of ¹ H-NMR (CDCl₃) are: d 1.0 (tJ=7Hz, 3H), d 1.19 (t J=7Hz, 3H), 3.48 (s, 2H); characteristic peaks of¹ H-NMR in DMSO-d₆ are: d 6.37 (d J=8.4Hz, 2H), 6.7 (s, 1H) 6.85 (dJ=8.4Hz, 2H), 7.5 (m, 2H), 8.02 (s, 1H, 8.03(s, 1H), 8.14 (d, 1H), 8.17(d, 1H).

Synthesis Example 4

The compound comp 4 and Inv 12 were prepared according to Scheme III.##STR65## Preparation of f'

A mixture of (d) (18.6 g, 0.04 mol), the oxime (e') (14.0 g, 0.04 mol),acetonitrile (300 mL) and water (300 mL) were stirred and cooled to 10°C. Acetic anhydride (13.0 g, 0.13 mol) was added, followed bytriethylamine (23.0 g 0.23 mol). A yellow-green solid resulted and themixture was stirred at 25° C. for 2 h, then at 80° C. for 0.5 h. Thelight green solid was collected, washed well with methanol and air driedat 25° C. (14.7 g, 53%).

Infrared analysis (IR KBr) showed the presence of the phthalimide groupat 1709 cm⁻¹.

Preparation of (g')

A mixture of the phthalimide dye f' (2.0 g, 3 mmol), 31% HBr in aceticacid (10 mL), 49% aqueous HBr (10 mL) and trifluoroacetic acid (1 mL)was stirred in a sealed glass vessel at 150-160° C. for 2 h. Completesolution was obtained. The mixture was allowed to cool to 25° C. (aprecipitate formed at 90° C.). Methanol (50 mL) was added to themixture, and the solid yellow dye collected by filtration. The dye wasrefluxed with methanol (50 mL), collected and dried in vacuo at 100° C.

IR (KBR) did not show the presence of the phthalimido group at 1709cm⁻¹.

Preparation of Comp 4 (h')

The dye (g') (1.25 g, 2mmol) and dimethylsulfoxide (DMSO) (10 mL) werecombined and sonicated for a few minutes. The ester-acid (c) (0.56 g, 2mmol), 4-N,N-dimethylaminopyridine (DMAP) (0.48 g, 4mmol) and1,5-diazabicyclo[4.3.0]non-5-ene (DBN) (0.5 g, 4 mmol) were added andthe mixture again sonicated again for a few minutes. Finally,2-chloro-N-methylpyridinium trifluoromethanesulfonate (1.10 g, 4 mmol)was added and the mixture stirred at 25° C. for 4 h. The mixture wasfiltered to remove a small amount of green insoluble material that wasdiscarded. To the filtrate was added 30% aqueous NaCl (125 mL) and theprecipitated orange product collected, washed well with water, thencarefully with methanol. The solid was air dried at 25° C. The crude dyewas dissolved in hot methanol (200 mL) and treated with decolorizingcarbon. The filtrate was placed under vacuum to induce crystallization,then the vacuum was removed and the filtrate cooled to 10° C. tocomplete crystallization of the dye. The purified dye was collected,washed with methanol and dried in vacuo at 25° C. 90.59 g, 36%).

Silica gel thin-layer chromatography (TLC) (90 methylene chloride/10methanol) showed essentially one spot, Rf=0.44.

Fast Atom Bombardment (FAB) mass spectrometry gave a large m/z=821 forthe desired dye (h').

Preparation of Inv 12

The dye Comp 4, (h'), (0.59 g, 0.72 mmol), methanol (200 mL) and 0.25 Nsodium hydroxide (20 mL, 5 mmol) were stirred at 25° C. for 25 h. Highpressure liquid chromatography (HPLC) with diode array detectionsuggested that ester interchange from the parent ethyl ester dye to themethyl ester dye preceded saponification to the sodium carboxylate dye.Preparatory HPLC provided a sample (470 mg) that was rich in the desiredsodium carboxylate dye (FAB MS, ¹ H NMR). NMR suggested that the dye waspresent in at least 85% purity.

Synthesis of Example V

The synthesis of Inv 32 was performed according to Scheme IV

Preparation of Intermediate (n)

To a stirred suspension of 21.4 g of aniline and 46 g of potassiumcarbonate in 300 mL of acetonitrile under a nitrogen atmosphere wasadded 50 g of ethyl-2-bromoproprionate. The reaction mixture wasrefluxed under nitrogen for 2 days, the solution was cooled, and thesalt was filtered out. The filtrate was poured into dichloromethane andwashed with aqueous sodium bicarbonate solution, then washed with water.Anhydrous sodium sulfate was added and then the dichloromethane solutionwas filtered. The filtrate was distilled under vacuum to give acolorless oil. 37.2 g of this oil was added to 200 mL of acetonitriletogether with 42 g of potassium carbonate and heated to reflux undernitrogen for 0.5 hour. 41.7 g of ethyl bromoacetate was then added andthe mixture was refluxed for 6 days. The mixture was then cooled, andthe salt was filtered. The product was taken up in dichloromethane,washed with aqueous sodium bicarbonate solution, washed again withwater, dried over anhydrous sodium sulfate, and filtered. The filtratewas concentrated and distilled to give 20.8 g of the desired anilinediester.

The diester (5.6 g, 0.02 mol) was added to a solution of chlorosulfonicacid (11.6 g, 0.1 mol) in dichloromethane (50 mL) and stirred at 25° C.for 8 h, and then at reflux for 4 h. Thionyl chloride (11.8 g, 0.1 mol)was added and the mixture heated at reflux for another 4 h. The mixturewas carefully added to ice water. The aqueous layer was discarded andthe dichloromethane layer concentrated at reduced pressure to give anoil. This oil was extracted into diethyl ether (50 mL) and the organiclayer washed five times with 30% aqueous sodium chloride. A trace ofsodium bicarbonate added to the ether layer, and this solutionsimultaneously treated with magnesium sulfate and silica gel (ICN04530). The ether was removed at reduced pressure to give the sulfonylchloride (82% yield, 6.2 g) intermediate (n).

Preparation of Intermediate (o)

A mixture of the intermediate (g) as described in example 1 (2.0 g, 3.2mmol), DMSO (40 mL), DMF (20 mL) and triethylamine (0.65 g, 6.4 mmol)was warmed to 50° C. Heating was discontinued and a solution ofintermediate (n) (1.21 g, 3.2 mmol) and DMF (20 mL) was added, followedby additional triethylamine (0.65 g, 6.4 mmol). The reaction mixture wasstirred at 25° C. for 16 h. The mixture was filtered and water (350 mL)was added to the filtrate to precipitate a yellow solid. A few drops ofHCl (37%) were added to make the pH ca. 4.0. The yellow solid wascollected, washed with water and dried in vacuo to give the crude dye(1.89 g). The crude dye was slurried in THF and filtered, then slurriedin ethanol, filtered and dried in vacuo at 25° C. to give a 75/25mixture (1.65 g) of the desired intermediate (o) and the startingmaterial intermediated (g) ##STR66## Prepartion of INV 32

To the mixture of intermediate (o) and intermediate (g) was added (1.5g), acetic acid (6 g, 0.1 mol), water (1.8 g, 0.1 mol) andmethanesulfonic acid (0.16 g, 1.7 mmol) was heated at reflux for 3 h.Sodium hydroxide (0.68 g, 1.7 mmol) was added to neutralize themethanesulfonic acid, and water was (200 mL) was added to precipitatethe crude product. The crude dye was slurried in ethanol and dried invacuo to give 1.06 g. This material was dissolved in acetic acid (10 mL)and methanol (100 mL) was added to initiate slow fractionalcrystallization. A fraction (200 mg) was estimated to contain ca. 85% ofthe desired INV 32 by diode array HPLC, FAB MS, ¹ H and ¹³ C NMR. Theremainder of the sample was composed of related partial hydrolysishalf-ester/half-acid intermediates.

Examples illustrating the beneficial use of these fragmentable electrondonating sensitizer compounds in silver halide emulsions are given inthe following:

EXAMPLE 1

An AgBrI tabular silver halide emulsion (Emulsion T-1) was preparedcontaining 4.05% total I distributed such that the central portion ofthe emulsion grains contained 1.5% I and the perimeter area containedsubstantially higher I, as described by Chang et. al., U.S. Pat. No.5,314,793. The emulsion grains had an average thickness of 0.123 μm andaverage circular diameter of 1.23 μm. The emulsion was sulfur sensitizedby adding 1.2×10⁻⁵ mole /Ag mole of(1,3-dicarboxymethyl-1,3-dimethyl-2-thiourea, DCT) at 40° C., thetemperature was then raised to 60° C. at a rate of 5° C./3 min and theemulsion held for 20 min before cooling to 40° C. This chemicallysensitized emulsion was then used to prepare the experimental coatingvariations indicated in Table I. All of these experimental coatingvariations contained the hydroxybenzene, 2,4-disulfocatechol (HB3) at aconcentration of 13 mmole/mole Ag, added to the melt before any furtheraddenda. The fragmentable electron donating sensitizer (FED) compoundand a conventional spectral sensitizing dye D-I or D-II were premixed inmethanol solution at the relative concentrations indicated in Table I(listed as a percentage of the sum total amount of dye and two-electrondonating sensitizer compound added) and added to the emulsion. At thetime of FED sensitizer addition, the emulsion melts had a VAg of 85-90mV and a pH of 6.0. Additional water, gelatin, and surfactant were thenadded to the emulsion melts. After 5 min at 40° C., an additional volumeof 4.3% gelatin was then added to give a final emulsion melt thatcontained 216 grams of gel per mole of silver. These emulsion melts werecoated onto an acetate film base at 1.61 g/m² of Ag with gelatin at 3.22g/m². The coatings were prepared with a protective overcoat whichcontained gelatin at 1.08 g/m², coating surfactants, and abisvinylsulfonylmethyl ether as a gelatin hardening agent.

For photographic evaluation, each of the coating strips was exposed for0.1 sec to a 365 nm emission line of a Hg lamp filtered through a KodakWratten filter number 18A and a step wedge ranging in density from 0 to4 density units in 0.2 density steps. The exposed film strips weredeveloped for 6 min in Kodak Rapid X-ray Developer (KRX). S₃₆₅, relativesensitivity at 365 nm, was evaluated at a density of 0.2 units abovefog.

The data in Table I compare the photographic sensitivities for emulsionscontaining various combinations of fragmentable electron donatingsensitizer compound with a conventional blue or red spectral sensitizingdye. For this exposure, relative sensitivity was set equal to 100 forthe control emulsion coating with no dye or fragmentable electrondonating sensitizer agent added. The addition of conventionalsensitizing dyes D-I or D-II cause some sensitivity decrease relative tothe undyed control (tests nos. 2 and 3) due to desensitization. Improvedsensitivity for the 365 nm exposure was shown for the examples whichcontained mixtures of D-I and a fragmentable electron donatingsensitizing agent (test nos. 4-15). The data in Table I show that at theoptimum concentrations Inv 8, 9, 10, 11, and 13 gave a factor of 1.2 to1.5 sensitivity increase relative to the comparison emulsion coatingcontaining only D-I. These sensitivity increases were accompanied byvery small increases in fog. Sensitivity increases relative to thecomparison (test no 2) of a factor of 1.9 were also found when thefragmentable electron donating sensitizer is used in combination with aconventional red sensitizing dye. However, somewhat larger increases infog were obtained with the inventive compounds when the red sensitizingdye D-II was present. Overall, these results show that the fragmentableelectron donating sensitizer can remove dye desensitization caused byconventional sensitizing dyes, and can give additional increases inphotographic sensitivity.

The Inv's 8, 9, 10, 11 and 13 in the Table contain the fragmentableelectron donating moiety XY. As indicated in (copending patentapplication Serial No., filed concurrently herewith, attorney docket No.69500), the XY groups in these sensitizing agents have one electronoxidation potentials E₁ which are less positive than 1.4 V and uponoxidation, fragment to give CO₂ and a corresponding neutral radical, andthe neutral radical. Related sensitizer compounds in which the XY groupdoes not fragment are less effective at increasing emulsion sensitivity.The comparison Comp 2, for example, contains an XY moiety that does notfragment upon oxidation, and thus does not satisfy criterion 2 of ourinvention. This compound (test no 15, 16, 17) gave no speed increasewhen used in combination with a conventional spectral sensitizing dye,but instead led to a speed decrease.

                                      TABLE I                                     __________________________________________________________________________    Speed and fog results for combinations of FED and blue or red                 sensitizing dye on Emulsion T-1                                               Total                                                                                       Amount of           Amount of                                                 Sensitizing         FED in                                                    Dye and             mixture Type of Sensitizing Dye Used        Test                                                                             FED added                                                                            Type of                                                                           % of total                                                                          D-I    D-II                                               No.                                                                              (mmol/mol Ag)                                                                        FED Dye conc                                                                            S.sub.365                                                                        Fog S.sub.365                                                                        Fog Remarks                                     __________________________________________________________________________    1  0.00   --  --    100                                                                              0.07                                                                              100                                                                              0.07                                                                              control                                     2  0.88   --  --     95                                                                              0.06                                                                               65                                                                              0.12                                                                              comparison                                  3  0.82   --  --     95                                                                              0.06                                                                               73                                                                              0.11                                                                              comparison                                  4  0.88   Inv 8                                                                             0.5   129                                                                              0.09                                                                              -- --  invention                                   5  0.82   Inv 9                                                                             0.1   120                                                                              0.06                                                                              107                                                                              0.19                                                                              invention                                   6  0.88   Inv 10                                                                            0.5   120                                                                              0.06                                                                              110                                                                              0.21                                                                              invention                                   7  0.88   Inv 13                                                                            0.05  -- --  123                                                                              0.24                                                                              invention                                   8  0.88   Inv 13                                                                            0.5   148                                                                              0.08                                                                              -- --  invention                                   9  0.88   Inv 13                                                                            1.0   148                                                                              0.09                                                                              -- --  invention                                   10 0.88   Inv 11                                                                            0.05  126                                                                              0.08                                                                              -- --  invention                                   11 0.88   Inv 11                                                                            0.1   135                                                                              0.07                                                                              -- --  invention                                   12 0.88   Inv 11                                                                            0.5   151                                                                              0.10                                                                              -- --  invention                                   13 0.88   Inv 11                                                                            1.0   151                                                                              0.11                                                                              -- --  invention                                   14 0.88   Inv 11                                                                            5.0   151                                                                              0.22                                                                              -- --  invention                                   15 0.88   Comp 2                                                                            1.0    95                                                                              0.10                                                                              -- --  comparison                                  16 0.88   Comp 2                                                                            5.0    89                                                                              0.10                                                                              -- --  comparison                                  17 0.88   Comp 2                                                                            10.0   85                                                                              0.13                                                                              -- --  comparison                                  __________________________________________________________________________     ##STR67##                                                                     ##STR68##                                                                    ?                                                                         

EXAMPLE 2

An AgrI tabular silver halide emulsion (Emulsion T-2) was preparedcontaining 4.05% total I distributed such that the central portion ofthe emulsion grains contained 1.5% I and the perimeter area containedsubstantially higher I, as described by Chang et. al., U.S. Pat. No.5,314,793. The emulsion grains had an average thickness of 0.116 μm andaverage circular diameter of 1.21 μm. This emulsion was precipitatedusing deionized gelatin. The emulsion was sulfur sensitized by adding8.5×10-6 mole 1,3-dicarboxymethyl-1,3-dimethyl-2-thiourea/mole Ag at 40°C.; the temperature was then raised to 60° C. at a rate of 5° C./3 minand the emulsions held for 20 min before cooling to 40° C. Thechemically sensitized emulsion was then used to prepare coatingscontaining combinations of the fragmentable two-electron-donatingsensitizing agent Inv 14 and spectral sensitizing dyes D-I, D-II, andD-III. In addition, some coatings were prepared containing thenon-fragmenting comparison Comp 3 and the spectral sensitizing dyes D-Iand D-II. As indicated in Table II, some of the experimental coatingvariations contained the hydroxybenzene, 2,4-disulfocatechol (HB3) at aconcentration of 13 mmole/mole Ag, added to the melt before the additionof any sensitizing dye compounds. The total concentration of dye used,that is the sum of the amounts of conventional spectral sensitizer plusfragmentable electron donating sensitizer, was 0.91 or 0.86 mmole/moleAg. The fragmentable electron donating sensitizer compounds were addedto the emulsion at 40° C. and the coatings were prepared and tested asdescribed in Example 1, except that the additional gelatin used toprepare the coatings described in Table II was deionized gelatin.

Additional testing was carried but to determine the response of thecoatings described in Table II to a spectral exposure. Each of thecoating strips was exposed for 0.1 sec to a 3000 K color temperaturetungsten lamp filtered to give an effective color temperature of 5500 Kand further filtered through a Kodak Wratten filter number 2B and a stepwedge ranging in density from 0 to 4 density units in 0.2 density steps.This filter passes only light of wavelengths longer than 400 nm, thusgiving light absorbed mainly by any sensitizing dyes present. Theexposed film strips were developed for 6 min in Kodak Rapid X-rayDeveloper (KRX). S_(WR2) B, relative sensitivity for this Kodak Wrattenfilter 2B exposure, was evaluated at a density of 0.2 units above fog.For this exposure, for each dye used, the relative sensitivity was setequal to 100 for the control coating with no fragmentable electrondonating compound added.

The data in Table II show for the emulsions containing the blue D-I, redD-II, or green D-III spectral sensitizing dye that the presence of thefragmentable two-electron donating sensitizer Inv 14 gave photographicsensitivity advantages at all concentrations examined. For the bluesensitized emulsion without added HB3 the optimum concentration of Inv14 gave a factor of 1.7 sensitivity gain for the 365 nm exposurerelative to the comparison (test no 2). This sensitivity increase occurswith a slight increase in fog. The amount of fog observed for the bluesensitized emulsion was minimized for the emulsions in which HB3 isadded. Speed increases for the 365 nm exposure up to a factor of 1.6were also obtained for the green and red sensitized emulsions but with amodest fog increase. The data for the Kodak Wratten 2B exposure showthat the use of the two electron donating sensitizer Inv 14 also gavesensitivity gains for spectral exposures of the blue, red, and greendyed emulsions. In comparison no instrinsic or spectral speed gains wereobserved for the blue and red dyed coatings containing Comp 3, acomparison compound consisting of a sensitizing dye linked to an XYmoiety that does not fragment. ##STR69##

                                      TABLE II                                    __________________________________________________________________________    Speed and fog results for combinations of Inv 14 mixed with                   blue or red sensitizing dye on Emulsion T-2, Black and White Format                       Amount                                                                             Amount                                                                   of Inv 14                                                                          of Comp                                                         Total Amount of                                                                        in   3 in       Amount of                                            Sensitizing Dye                                                                        mixture                                                                            mixture                                                                            Type of                                                                             HB3   Photographic                                Test                                                                             and FED added                                                                          % of total                                                                         % of total                                                                         Sensitizing                                                                         added (10.sup.-3                                                                    Sensitivity                                 No.                                                                              (10.sup.-3 mol/mol Ag)                                                                 Dye conc                                                                           Dye conc                                                                           Dye Used                                                                            mol/mol Ag)                                                                         S.sub.365                                                                        S.sub.WR2B                                                                        Fog                                                                              Remarks                           __________________________________________________________________________     1 0        0    0    none   0    100                                                                              --  0.06                                                                             control                            2 0.91     0    0    I      0    100                                                                              100 0.07                                                                             comparison                         3 0.91     1    0    I      0    174                                                                              159 0.15                                                                             invention                          4 0.91     2    0    I      0    170                                                                              159 0.20                                                                             invention                          5 0.91     5    0    I      0    151                                                                              148 0.31                                                                             invention                          6 0.91     0    0    I     13    120                                                                              123 0.07                                                                             comparison                         7 0.91     1    0    I     13    166                                                                              159 0.11                                                                             invention                          8 0.91     2    0    I     13    166                                                                              159 0.14                                                                             invention                          9 0.91     5    0    I     13    159                                                                              148 0.20                                                                             invention                         10 0.91     0    1    I     13    120                                                                              123 0.07                                                                             comparison                        11 0.91     0    10   I     13    120                                                                              123 0.07                                                                             comparison                        12 0.86     0         II    13     85                                                                              100 0.11                                                                             comparison                        13 0.86       0.2                                                                              0    II    13    135                                                                              162 0.28                                                                             invention                         14 0.86       0.5                                                                              0    II    13    129                                                                              159 0.40                                                                             invention                         15 0.86       1.0                                                                              0    II    13    120                                                                              145 0.51                                                                             invention                         16 0.86     0      0.5                                                                              II    13     82                                                                               97 0.12                                                                             comparison                        17 0.86     0      1.0                                                                              II    13     78                                                                               97 0.12                                                                             comparison                        18 0.86     0    0    III   13     94                                                                              100 0.09                                                                             comparison                        19 0.86       0.2                                                                              0    III   13    115                                                                              110 0.57                                                                             invention                         20 0.86       1.0                                                                              0    III   13    135                                                                              105 0.61                                                                             invention                         __________________________________________________________________________

EXAMPLE 3

An AgBrI tabular silver halide emulsion (Emulsion T-2) was preparedcontaining 4.05% total I distributed such that the central portion ofthe emulsion grains contained 1.5% I and the perimeter area containedsubstantially higher I as described by Chang et. al., U.S. Pat. No.5,314,793. The emulsion grains had an average thickness of 0.116 μm andaverage circular diameter of 1.21 μm. In addition, the following tabularemulsions were prepared each having a uniform halide distribution:Emulsion T-3, an AgBrI tabular emulsion with 1.5% total iodide, havingan average thickness of 0.095 μm and an average circular diameter of1.27 μm; emulsion T-4, an AgBrI tabular emulsion with 3.0% total iodide,having an average thickness of 0.097 μm and an average circular diameterof 1.14 μm; and emulsion T-5, an AgBr tabular emulsion having an averagethickness of 0.084 μm and an average circular diameter of 1.40 μm.Emulsions T-2 through T-5 were all precipitated using deionized gelatin.The emulsions were sulfur sensitized by adding1,3-dicarboxymethyl-1,3-dimethyl-2-thiourea at 40° C.; the temperaturewas then raised to 60° C. at a rate of 5° C./3 min and the emulsionsheld for 20 min before cooling to 40° C. The amounts of the sulfursensitizing compound used were 8.5×10⁻⁶ mole/mole Ag for emulsion T-2,1.05×10⁻⁵ mole/mole Ag for emulsion T-3, 1.5×10⁻⁵ mole/mole Ag foremulsion T-4 and 1.6×10⁻⁵ mole/mole Ag for emulsion T-5. Thesechemically sensitized emulsions were then used to prepare theexperimental coating variations indicated in Table III.

All of the experimental coating variations in Table III contained thehydroxybenzene, 2,4-disulfocatechol (HB3) at a concentration of 13mmole/mole Ag, added to the melt before any further addenda. Thefragmentable electron donating sensitizer Inv 11 was mixed with the bluesensitizing dye D-I or the red sensitizing dye D-II at various moleratios in methanol solution and then added to the emulsion at 40° C. Thecoatings were prepared as described in Example 1, except that theadditional gelatin used to prepare the coatings described in Table IIIwas deionized gelatin. The coatings were tested for their sensitivity toa 365 nm exposure as described in Example 1. For this exposure, relativesensitivity was set equal to 100 for each of the control emulsioncoatings with no dye or fragmentable electron donating compound added.

The data in Table III show that some loss of sensitivity for a 365 nmexposure was generally observed upon the addition of the blue D-I or redD-II sensitizing dye, indicating dye desensitization. Thisdesensitization was particularly severe for the red sensitizing dye onemulsions T-3, T-4, and T-5. The presence of the fragmentable electrondonating sensitizer Inv 11 significantly increased the 365 nm speed forall of the dyed emulsions, which indicates that the two electrondonating compound is effective in ameliorating the dye desensitization.For the combination of the fragmentable electron donating sensitizer Inv11 with the red sensitizing dye D-II, larger fog increases were observedfor emulsions T-2, T-3, and T-5 at the higher Inv 11 concentration.These results indicate that the optimum Inv 11 concentration for thesered-dyed emulsions lies between the two concentrations examined.

                                      TABLE III                                   __________________________________________________________________________    Speed and fog results for combinations of dye and blue or red                 sensitizing dye on Emulsion T-1                                                             Total Amount of                                                               Amount of                                                                           Inv 11 in                                                         Type of                                                                             Dye added                                                                           Mixture                                                                            Relative                                             Test                                                                             Emulsion                                                                           Sensitizing                                                                         (10.sup.-3                                                                          % of total                                                                         Sensitivity                                          No.                                                                              Type Dye Used                                                                            mol/mol Ag)                                                                         conc S.sub.365                                                                        Fog                                                                              Remarks                                        __________________________________________________________________________    1  T-2  none  0     0    100                                                                              0.07                                                                             control                                        2  T-2  I     0.88  0.0% 89 0.06                                                                             comparison                                     3  T-2  I     0.88  0.2% 118                                                                              0.06                                                                             invention                                      4  T-2  I     0.88  1.0  126                                                                              0.07                                                                             invention                                      5  T-2  II    0.52  0.0  60 0.09                                                                             comparison                                     6  T-2  II    0.52  0.3  95 0.16                                                                             invention                                      7  T-2  II    0.52  1.7  -- 1.01                                                                             invention                                      8  T-3  none  0     0    100                                                                              0.07                                                                             control                                        9  T-3  I     0.72  0.0  33 0.06                                                                             comparison                                     10 T-3  I     0.72  0.2  50 0.07                                                                             invention                                      11 T-3  I     0.72  1.0  52 0.07                                                                             invention                                      12 T-3  II    0.43  0.0  19 0.09                                                                             comparison                                     13 T-3  II    0.43  0.3  11 0.10                                                                             invention                                      14 T-3  II    0.43  1.7  59 0.59                                                                             invention                                      15 T-4  none  0     0    100                                                                              0.07                                                                             control                                        16 T-4  I     1.01  0.0  13 0.06                                                                             comparison                                     17 T-4  I     1.01  0.2  32 0.06                                                                             invention                                      18 T-4  I     1.01  1.0  35 0.06                                                                             invention                                      19 T-4  II    0.61  0.0  1.6                                                                              0.09                                                                             comparison                                     20 T-4  II    0.61  0.3  2.8                                                                              0.10                                                                             invention                                      21 T-4  II    0.61  1.7  11 0.17                                                                             invention                                      22 T-5  none  0     0    100                                                                              0.07                                                                             control                                        23 T-5  I     0.88  0.0  50 0.07                                                                             comparison                                     24 T-5  I     0.88  0.2  91 0.07                                                                             invention                                      25 T-5  I     0.88  1.0  112                                                                              0.07                                                                             invention                                      26 T-5  II    0.52  0.0  8.3                                                                              0.09                                                                             comparison                                     27 T-5  II    0.52  0.3  22 0.10                                                                             invention                                      28 T-5  II    0.52  1.7  -- 0.93                                                                             invention                                      __________________________________________________________________________

EXAMPLE 4

The sulfur sensitized emulsion T-2 was used to prepare coatingscontaining combinations of the fragmentable electron-donatingsensitizing agent Inv 12 and blue spectral sensitizing dye D-I. Theseexperimental coating variations contained the hydroxybenzene2,4-disulfocatechol (HB3) at a concentration of 13 mmole/mole Ag, addedto the melt before the addition of any sensitizing dye compounds. Thetotal concentration of dye used, that is the sum of the amounts ofconventional spectral sensitizer plus fragmentable electron donatingsensitizer, was 0.91 mmole/mole Ag. The fragmentable electron donatingcompounds were added to the emulsion at 40° C. and the coatings wereprepared and tested as described in Example 2.

The data in Table IV show for the emulsions containing the blue D-Ispectral sensitizing dye that the presence of the fragmentable electrondonating sensitizer Inv 12 gave photographic sensitivity advantages atall concentrations examined. These sensitivity advantages were obtainedfor both instrinsic exposures of the silver halide at 365 nm andspectral exposures of the blue sensitizing dye, using the Kodak Wratten2B filter.

                                      TABLE IV                                    __________________________________________________________________________    Speed and fog results for combinations of Inv 12 and                          blue sensitizing dye on Emulsion T-2                                             Total                                                                         Amount of                                                                           Amount                                                                  Sensitizing                                                                         of Inv 12                                                               Dye and                                                                             in         Amount of                                                    FED added                                                                           mixture                                                                            Type of                                                                             HB3 added                                                                           Photographic                                        Test                                                                             (10.sup.-3                                                                          (% of                                                                              Sensitizing                                                                         (10.sup.-3                                                                          Sensitivity                                         No.                                                                              mol/mol/Ag)                                                                         total)                                                                             Dye Used                                                                            mol/mol Ag)                                                                         S.sub.365                                                                        S.sub.WR2B                                                                        Fog                                                                              Remarks                                   __________________________________________________________________________    1  0.91  0    I     13    100                                                                              100 0.05                                                                             comparison                                2  0.91  1    I     13    145                                                                              132 0.08                                                                             invention                                 3  0.91  2    I     13    145                                                                              135 0.11                                                                             invention                                 4  0.91  5    I     13    138                                                                              132 0.17                                                                             invention                                 __________________________________________________________________________

EXAMPLE 5

Two cubic emulsions with uniform halide composition were precipitatedusing deionized gelatin. Emulsion C-1 was a AgBrI emulsion with a 3% Icontent and a cubic edge length of 0.47 mm and emulsion C-2 was an AgBremulsion with a cubic edge length of 0.52 mm. The emulsions were sulfursensitized by adding 1,3-dicarboxymethyl-1,3-dimethyl-2-thiourea at 40°C.; the temperature was then raised to 60° C. at a rate of 5° C./3 minand the emulsions held for 20 min before cooling to 40° C. The amountsof the sulfur sensitizing compound used were 1.0×10⁻⁵ mole/mole Ag foremulsion C-1, and 6.0×10⁻⁶ mole/mole Ag for emulsion C-2. Theseemulsions were then used to prepare the experimental coating variationslisted in Table V. These experimental coating variations contained thehydroxybenzene 2,4-disulfocatechol (HB3) at a concentration of 13mmole/mole Ag, added to the melt before the addition of any sensitizingdye compounds. The emulsions were then dyed with mixtures of thesensitizing dyes D-I or D-II with the fragmentable electron donatingsensitizing agent Inv 11 in the manner described in Example 1. Coatingswere then prepared and tested as described in Example 1 except that theadditional gelatin used to prepare the coatings described in Table V wasdeionized gelatin.

The data in Table V show that addition of the fragmentable electrondonating sensitizing agent Inv 11 to these dyed cubic emulsions gavesubstantial 365 nm speed increases with only small fog increases in allcases examined. The presence of the sensitizing dye D-I desensitizedboth emulsions C-1 and C-2 while the sensitizing dye D-II desensitizedemulsion C-2 but gave a small increase in 365 nm sensitivity foremulsion C-1. Nevertheless, in all cases, 365 nm sensitivities for thedyed emulsions containing the Inv 11 were higher than the sensitivity ofthe undyed control. In the most favorable cases (tests 7-9), thissensitivity increase was a factor of 2.5×. These data indicate that theelectron donating sensitizing agent Inv 11 can not only ameliorate dyedesensitization but also increase the intrinsic sensitivity of dyedemulsions to light absorbed by the silver halide crystals to a levelbeyond that of the undyed control.

                                      TABLE V                                     __________________________________________________________________________    Speed and fog results for combinations of Inv 11 and blue or red              sensitizing dye on Emulsions C-1 and C-2                                                    Total Amount                                                                  of Sensitizing                                                                       Amount of                                                              Dye    FED in                                                           Type of                                                                             and FED                                                                              mixture %                                                                          Photographic                                        Test                                                                             Emulsion                                                                           Sensitizing                                                                         added (10.sup.-3                                                                     of total                                                                           Sensitivity                                         No.                                                                              Type Dye   mol/mol Ag)                                                                          Dye conc                                                                           S.sub.365                                                                        Fog                                                                              Remarks                                       __________________________________________________________________________    1  C-1  none  0.00   0    100                                                                              0.09                                                                             control                                       2  C-1  D-I   0.66   0    60 0.11                                                                             comparison                                    3  C-1  D-I   0.66   1.0  240                                                                              0.12                                                                             invention                                     4  C-1  D-I   0.66   2.0  246                                                                              0.12                                                                             invention                                     5  C-1  D-I   0.66   4.0  240                                                                              0.12                                                                             invention                                     6  C-1  D-II  0.44   0    129                                                                              0.12                                                                             comparison                                    7  C-1  D-II  0.44   0.2  251                                                                              0.25                                                                             invention                                     8  C-1  D-II  0.44   0.5  251                                                                              0.28                                                                             invention                                     9  C-1  D-II  0.44   1.0  257                                                                              0.27                                                                             invention                                     10 C-2  none  0.00   0    100                                                                              0.06                                                                             control                                       11 C-2  D-I   0.59   0    60 0.07                                                                             comparison                                    12 C-2  D-I   0.59   1.0  162                                                                              0.08                                                                             invention                                     13 C-2  D-I   0.59   2.0  170                                                                              0.08                                                                             invention                                     14 C-2  D-I   0.59   4.0  170                                                                              0.09                                                                             invention                                     15 C-2  D-II  0.40   0    65 0.08                                                                             comparison                                    16 C-2  D-II  0.40   0.2  151                                                                              0.20                                                                             invention                                     17 C-2  D-II  0.40   0.5  166                                                                              0.24                                                                             invention                                     18 C-2  D-II  0.40   1.0  159                                                                              0.28                                                                             invention                                     __________________________________________________________________________

EXAMPLE 6

The AgBrI tabular silver halide emulsion T-2 from Example 2 wasoptimally chemically and spectrally sensitized by adding NaSCN, 1.07mmole of the blue sensitizing dye D-I per mole Ag, Na₃ Au(S₂ O₃)₂ ·2H₂O, Na₂ S₂ O₃ ·5H₂ O, and a benzothiazolium finish modifier and thensubjecting the emulsion to a heat cycle to 65° C. The hydroxybenzene2,4-disulfocatechol (HB3) at a concentration of 13×10⁻³ mole/mole Ag wasadded to the emulsion melt before the start of the chemicalsensitization procedure. The fragmentable electron donating sensitizingagent Inv 11 was added to the emulsion either after the chemicalsensitization procedure or as an additional component in the chemicalsensitization procedure, added after the dye D-I. The variationsexamined are given in Table VI.

The melts were prepared for coating by adding additional water,deionized gelatin, coating surfactants, and the antifoggant andstabilizer tetraazaindene at 1.75 gm/mole Ag. Coatings were prepared bycombining the emulsion melts with a melt containing deionized gelatinand an aqueous dispersion of the cyan-forming color coupler CC-1 andcoating the resulting mixture on acetate support. The final coatingscontained Ag at 0.81 g/m², coupler at 1.61 g/m², and gelatin at 3.23g/m². The coatings were overcoated with a protective layer containinggelatin at 1.08 g/m², coating surfactants, and a bisvinylsulfonylmethylether as a gelatin hardening agent.

For photographic evaluation, each of the coating strips was exposed for0.01 sec to a 3000 K color temperature tungsten lamp filtered to give aneffective color temperature of 5500 K and further filtered through aKodak Wratten filter number 2B, and a step wedge ranging in density from0 to 4 density units in 0.20 density steps. This exposure gives lightabsorbed mainly by the blue sensitizing dye. The exposed film stripswere developed for 31/4 minutes in Kodak C-41 color developer. S_(WR2B),relative sensitivity for this filtered exposure, was evaluated at a cyandensity of 0.15 units above fog.

The data in Table VI show that the use of the fragmentable electrondonating sensitizing agent Inv 11 in this optimally sensitized,blue-sensitized emulsion in color format gave significant spectral speedgains with some small fog increases. The data also show that the Inv 11functioned well when added during the chemical sensitization or whenadded at the conclusion of the chemical sensitization procedure.##STR70##

                  TABLE VI                                                        ______________________________________                                        Speed and fog results for combinatins of Inv 11 dye with a blue               sensitized AgBrI T-grain Emulsion T-2 COLOR FORMAT                                 Amount of                                                                     of Inv 11                                                                     added     Position    Photographic                                       Test (10.sup.-6  mol/                                                                        of Inv 11   Sensitivity                                        No.  mol Ag)   Addition    S.sub.WR2B                                                                          Fog   Remarks                                ______________________________________                                        1    none      --          100   0.08  comparison                             2    1.5       after sensitization                                                                       145   0.09  invention                              3    4.5       after sensitization                                                                       159   0.30  invention                              4    1.5       in sensitization                                                                          132   0.10  invention                              5    4.5       in sensitization                                                                          148   0.15  invention                              ______________________________________                                    

EXAMPLE 7

The optimally sensitized, blue dyed tabular AgBrI emulsion T-2 asdescribed in Example 6 was used to prepare color format coatingscontaining the fragmentable two-electron donating sensitizing agents Inv11 and 14 and as described in Table VII. The antifoggant and stabilizertetraazaindene (TAI) was added to the melts of the chemically sensitizedemulsion as the first addenda at a concentration of 1.75 gm/mole Ag. Thefragmentable two-electron donating sensitizing agents were then added tothe emulsion melt. The melts were prepared for coating as described inExample 6 except that no additional TAI was added. The coating stripsobtained were then tested as described in Example 6.

The data in Table VII indicate that both Inv 11 and 14 and gavesignificant speed increases with only small fog increases when added tothis optimally sensitized, blue dyed emulsion. At equivalentconcentrations, Inv 14 gave slightly better speed and improved fogcompared to Inv 14. This comparison demonstrates the advantage of havingan X-Y moiety of higher first oxidation potential E₁ as the fragmentabletwo-electron donating species linked to the sensitizing dye.

                  TABLE VII                                                       ______________________________________                                        Speed and fog result for combinations of Inv 11 and Inv 14 dyes with          a blue sensitized AgBrI T-grain Emulsion T-2 COLOR FORMAT                                   Amount of                                                                     FED added   Photographic                                        Test  Type of (10.sup.-6  mol/                                                                          Sensitivity                                         No.   FED     mol Ag)     S.sub.WR2B                                                                          Fog    Remarks                                ______________________________________                                        1             none        100   0.08   comparison                             2     Inv 11  1.5         138   0.09   invention                              3     Inv 11  4.5         170   0.13   invention                              4     Inv 14  1.5         148   0.09   invention                              5     Inv 14  4.5         174   0.09   invention                              6     Inv 14  1.5         186   0.19   invention                              ______________________________________                                    

EXAMPLE 8

The sulfur sensitized emulsion AgBrI tabular emulsion T-1 was used toprepare coatings containing combinations of the compounds Inv 15 or Comp5 or with the blue spectral sensitizing dye D-I. The total concentrationof dye used, that is the sum of the amounts of conventional spectralsensitizer plus electron donating sensitizer, was 0.82 mmole/mole Ag.The compounds were added to the emulsion at 40° C. and the coatings wereprepared and tested as described in Example 1, except thatdisulfocatechol was not used in these coatings.

Table VIII shows that addition of the fragmentable electron donatingsensitizer Inv 15 to the blue-dyed emulsion T-1 causes moderateincreases in photographic sensitivity. This compound contains an XYmoiety that has an oxidation potential E₁ less positive than 1.4 V andthat fragments upon oxidation to give CO₂ and a corresponding neutralradical, thus satisfying the two criteria of our invention. However,this compound falls outside the most preferred category of ourinvention, since the neutral radical created has an oxidation potentialE₂ that is less negative than -0.7 V. Addition of the Comp 5 to theblue-dyed emulsion T-1 causes no increase in photographic sensitivity.This compound contains an XY moiety that has an oxidation potential E₁less positive than 1.4 V but does not satisfy the second criterion ofour invention, since this ester-containing XY moiety does not fragmentupon oxidation.

                  TABLE VIII                                                      ______________________________________                                        Speed and fog result for combinations of Inv 15 or Comp 5 and blue            sensitizing dye D-I on Emulsion T-1                                                         Total                                                                         Amount of Amount                                                              Sensitizing                                                                             of FED                                                     Type of  Dye and   in                                                         FED      FED added mixture                                                                              Photographic                                   Test Com-     (10.sup.-3  mol/                                                                        % of total                                                                           Sensitivity                                    No.  pound    mol Ag)   Dye Conc.                                                                            S.sub.365                                                                          Fog  Remarks                              ______________________________________                                        1    none     0.82      0      100  0.06 comparison                           2    Inv 15   0.82      5      107  0.06 invention                            3    Inv 15   0.82      10     107  0.06 invention                            4    Inv 15   0.82      20     107  0.06 invention                            5    Comp 5   0.82      5      100  0.08 comparison                           6    Comp 5   0.82      20     94   0.13 comparison                           ______________________________________                                    

EXAMPLE 9

A cubic emulsion C-3 with uniform halide composition was precipitatedusing deionized gelatin. This emulsion was a AgBrI emulsion with a 3% Icontent and a cubic edge length of 0.24 mm. The emulsions was sulfursensitized by adding 2.4×10⁻⁵ mole/mole Ag of1,3-dicarboxymethyl-1,3-dimethyl-2-thiourea at 40° C.; the temperaturewas then raised to 60° C. at a rate of 5° C./3 min and the emulsion heldfor 20 min before cooling to 40° C. This emulsion was then used toprepare the experimental coating variations listed in Table IX. Theemulsion was dyed with mixtures of the blue sensitizing dye D-I with thecompounds Comp 5, Inv 15 or Inv 11, in the manner described in ExampleI. Coatings were then prepared and tested as described in Example Iexcept that the additional gelatin used to prepare the coatingsdescribed in Table IX was deionized gelatin and disulfo catechol was notused in these coatings.

The data in Table IX show that addition of the blue sensitizing dye tothe emulsion C-3 causes some decrease in sensitivity to a 365 nmexposure, indicating dye desensitization. All three of the compoundstested give significant speed gains on this small cubic emulsion,increasing the 365 nm sensitivity beyond that of the undyed emulsion andremoving the dye desensitization. All three of these compounds satisfythe first criterion of our invention, in that they contain an XY moietywith an oxidation potential E₁ that is less positive than 1.4 V.However, only Inv 11 and 15 are fragmentable electron donatingsensitizers and satisfy both criteria of our invention by containing XYmoieties that fragment upon oxidation. Table IX shows that the speedgain obtained with these two compounds is substantially greater than thespeed gain with Comp 5, which does not fragment upon oxidation. Finally,only Inv 11 satisfies the most preferred category of our invention inthat the neutral radical created upon oxidation and fragmentation of theXY moiety has an oxidation potential more negative than -0.7 V. Table IXshows clearly that this fragmentable two-electron donating sensitizerInv 11 gives the largest sensitivity increase of the three compoundstested.

                  TABLE IX                                                        ______________________________________                                        Speed and fog result for combinations of Comp 5, Inv 15 or Inv 11 and         blue sensitizing dye D-I on Emulsion C-3                                                    Total                                                                         Amount of Amount                                                              Sensitizing                                                                             of FED                                                     Type of  Dye and   in                                                         FED      FED added mixture                                                                              Photographic                                   Test Com-     (10.sup.-3  mol/                                                                        % of total                                                                           Sensitivity                                    No.  pound    mol Ag)   Dye Conc.                                                                            S.sub.365                                                                          Fog  Remarks                              ______________________________________                                        1    none     none      none   100  0.14 control                              2    none     1.16       0     68   0.16 comparison                           3    Comp 5   1.16      10     162  0.17 comparison                           4    Comp 5   1.16      20     195  0.18 comparison                           5    Inv 15   1.16      10     209  0.17 invention                            6    Inv 15   1.16      20     246  0.18 invention                            7    Inv 11   1.16       2     309  0.20 invention                            8    Inv 11   1.16       5     363  0.23 invention                            ______________________________________                                    

EXAMPLE 10

The sulfur sensitized emulsion T-2 described in Example 2 was used toprepare coatings containing combinations of the fragmentableelectron-donating sensitizer Inv 32 with red or green spectralsensitizing dyes D-II and D-III. These experimental coating variationscontained the hydroxybenzene HB3 at a concentration of 13 mmole/mole Ag,added to the melt before the addition of any sensitizing dye compounds.Some of the comparison coatings contained conventional blue sensitizerD-I in place of the blue fragmentable electron-donating sensitizer Inv32. The total concentration of dye used, that is the sum of the amountsof conventional spectral sensitizer plus two-electron donatingsensitizer, was 0.86 mmole/mole Ag. The two electron donating compoundswere added to the emulsion at 40° C. and the coatings were preparedfragmentable electron-donating sensitizer Inv 32 as described in Example2. Evaluation of the photographic sensitivity was carried out asdescribed in Example 1.

The data in Table X show that some loss of sensitivity for a 365 nmexposure was generally observed upon the addition of the green D-III orred D-II sensitizing dye (test no. 2 and 9), indicating dyedesensitization. This desensitization is not alleviated by the mixinglow concentrations of the conventional blue sensitizer D-I with dyesD-II or D-III (tests no. 3, 4, 5, 10, 11). Combining the fragmentableelectron-donating sensitizer Inv 32 into a mixture with D-II or D-IIIsignificantly increased the 365 nm speed for all of the dyed emulsions,which indicates that Inv 32 is effective in ameliorating the dyedesensitization. These speed increases occur with no increase in fog.

                                      TABLE X                                     __________________________________________________________________________    Speed and fog results for combinations of Inv 32 or                           blue sensitizing dye with red and green sensitizing dyes on Emulsion T-2               Total Amount of                                                                        Amount of                                                                           Amount of                                                Type of                                                                             Sensitizing Dye                                                                        Inv 32 in                                                                           D-I in                                                                              Photographic                                    Test                                                                             Sensitizing                                                                         and FED added                                                                          mixture                                                                             mixture                                                                             Sensitivity                                     No.                                                                              Dyes Used                                                                           (10.sup.-3 mol/mol Ag)                                                                 (% of total)                                                                        (% of total)                                                                        S.sub.365                                                                        Fog                                                                              Remarks                                   __________________________________________________________________________    1  none  0        0     0     100                                                                              0.05                                                                             control                                   2  II    0.86     0     0     71 0.11                                                                             comparison                                3  I and II                                                                            0.86     0     2     73 0.11                                                                             comparison                                4  I and II                                                                            0.86     0       6.4 74 0.11                                                                             comparison                                5  I and II                                                                            0.86     0     20    78 0.10                                                                             comparison                                6  II    0.86     0     0     91 0.11                                                                             invention                                 7  II    0.86       6.4 0     94 0.11                                                                             invention                                 8  II    0.86     20    0     105                                                                              0.11                                                                             invention                                 9  III   0.86     0     0     85 0.08                                                                             comparison                                10 I and III                                                                           0.86     0     2     89 0.08                                                                             comparison                                11 I and III                                                                           0.86     0       6.4 73 0.08                                                                             comparison                                12 III   0.86     2     0     95 0.08                                                                             invention                                 13 III   0.86       6.4 0     95 0.08                                                                             invention                                 __________________________________________________________________________

EXAMPLE 11

The optimally sensitized, blue-dyed tabular AgBrl emulsion T-2 asdescribed in Example 6 was used to prepare color format coatingscontaining the fragmentable electron donating sensitizing agent Inv 31or additional sensitizing dye D-I as described in Table IX. Theantifoggant and stabilizer tetraazaindene (TAI) was added to the meltsof the chemically sensitized emulsion as the first addendum at aconcentration of 1.75 gm/mole Ag. The fragmentable electron donatingsensitizing agent was then added to the emulsion melt. The melts wereprepared for coating as described in Example 6 except that no additionalTAI was added. The coating strips obtained were then tested as describedin Example 6.

The data in Table XI indicate that addition of the fragmentable electrondonating agent Inv 31 to this optimally sensitized blue-dyed emulsiongave substantial speed increases of 1.5 to 1.7× with essentially no fogincrease. As a comparison, the coating with only extra sensitizing dyeD-I added gave no speed increase.

                  TABLE XI                                                        ______________________________________                                        Speed and fog results for combinations of Inv 31 dye with a blue              sensitized AgBrl T-grain Emulsion T-2 in color format                                       Amount of                                                                     FED added   Photographic                                        Test  Type of (10.sup.-6  mol/                                                                          Sensitivity                                         No.   FED     mol Ag)     S.sub.WR2B                                                                          Fog    Remarks                                ______________________________________                                        1             none        100   0.07   comparison                             2     D-I     140          98   0.07   comparison                             3     Inv 31   14         148   0.08   invention                              4     Inv 31   45         159   0.09   invention                              5     Inv 31  140         166   0.11   invention                              ______________________________________                                    

This invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

What is claimed is:
 1. A photographic element comprising at least onesilver halide emulsion layer in which the silver halide is sensitizedwith a compound of formula

    Z-(L-XY).sub.k

wherein: Z is a light absorbing group; L is a linking group containing aleast one C, N, S, or O atom; and k is 1 or 2; and XY represents afragmentable electron donor moiety wherein:1) XY has an oxidationpotential between 0 and about 1.4 V; 2) X is an electron donor group; 3)Y is a leaving group other than hydrogen; and 4) the oxidized form of XYundergoes a bond cleavage reaction to give the radical X.sup.• and theleaving fragment Y.
 2. A photographic element comprising at least onesilver halide emulsion layer in which the silver halide is sensitizedwith a compound of formula

    Z-(L-XY).sub.k

wherein: Z is a light absorbing group; L is a linking group containing aleast one C, N, S, or O atom; and k is 1 or 2; and XY represents afragmentable electron donor moiety wherein:1) XY has an oxidationpotential between 0 and about 1.4 V; 2) X is an electron donor group; 3)Y is a leaving group other than hydrogen; 4) the oxidized form of XYundergoes a bond cleavage reaction to give the radical X.sup.• and theleaving fragment Y; and 5) the radical X.sup.• has an oxidationpotential more negative than about -0.7 V.
 3. A photographic elementaccording to claim 1 or claim 2, wherein Z is a spectral sensitizingagent.
 4. A photographic element according to claim 3, wherein thespectral sensitizing agent is a cyanine, merocyanine, styryl,hemicyanine, or complex cyanine dye.
 5. A photographic element accordingto claim 3, wherein the spectral sensitizing dye is represented by theformulae VIII-XII below: ##STR71## wherein: E₁ and E₂ represent theatoms necessary to form a substituted or unsubstituted hetero ring andmay be the same or different,each J independently represents asubstituted or unsubstituted methine group, q is a positive integer offrom 1 to 4, p and r each independently represents 0 or 1, D₁ and D₂each independently represents substituted or unsubstituted alkyl orunsubstituted aryl, and W₂ is a counterion as necessary to balance thecharge; ##STR72## wherein E₁, D₁, J, p, q and W₂ are as defined abovefor formula (VIII) and G represents ##STR73## wherein E₄ represents theatoms necessary to complete a substituted or unsubstituted heterocyclicnucleus, and F and F' each independently represents a cyano radical, anester radical, an acyl radical, a carbamoyl radical or an alkylsulfonylradical; ##STR74## wherein D₁, E₁, J, p, q and W₂ are as defined abovefor formula (VIII), and G₂ represents a substituted or unsubstitutedamino radical or a substituted or unsubstituted aryl radical; ##STR75##wherein D₁, E₁, D₂, E₁, J, p, q, r and W₂ are as defined for formula(VIII) above, and E₃ is defined the same as E₄ for formula (IX) above;##STR76## wherein D₁, E₁, J, G, p, q, r and W₂ are as defined above forformula (VIII) above and E₃ is as defined for formula (XI) above.
 6. Aphotographic element according to claim 1 or claim 2, wherein L containsan alkylene group, an arylene group, --O--, --S--, --C═O, --SO₂ --,--NH--, --P═O, or --N═.
 7. A photographic element according to claim 6,wherein L comprises a group of the formula: ##STR77## where c=1-30, andd=1-10.
 8. A photographic element according to claim 6, wherein L is ofthe formula: ##STR78## wherein e and f=1-30, with the proviso thate+f≦30.
 9. A photographic element according to claim 1 or claim 2,wherein X is of formula (I): ##STR79## wherein: m is 0 or 1;Z is O, S,Se or Te; Ar is an aryl group or a heterocyclic group; R₁ is R,carboxyl, amide, sulfonamide, halogen, NR₂, (OH)_(n), (OR')_(n) or(SR)_(n) ; where R' is alkyl or substituted alkyl; n is 1-3; R₂ is R orAr'; R₃ is R or Ar'; R₂ and R₃ together can form 5- to 8- membered ring;R₂ and Ar can be linked to form 5- to 8- membered ring; R₃ and Ar can belinked to form 5- to 8- membered ring; Ar' is an aryl group or aheterocyclic group; and R is a hydrogen atom or an unsubstituted orsubstituted alkyl group.
 10. A photographic element according to claim9, wherein X is selected from the group consisting of: ##STR80## whereinR is a hydrogen atom or a substituted or unsubstituted alkyl group. 11.A photographic element according to claim 1 or claim 2, wherein X is offormula (II): ##STR81## wherein: Ar is an aryl group or a heterocyclicgroup;R₄ is a substituent having a Hammett sigma value of -1 to +1; R₅is R or Ar'; R₆ is R or Ar'; R₇ is R or Ar'; R₅ and Ar can be linked toform 5- to 8- membered ring; R₆ and Ar can be linked to form 5- to 8-membered ring, in which case R₆ can comprise a hetero atom; R₅ and R₆can be linked to form 5- to 8- membered ring; R₆ and R₇ can be linked toform 5- to 8- membered ring; Ar' is an aryl group or a heterocyclicgroup; and R is a hydrogen atom or an unsubstituted or substituted alkylgroup.
 12. A photographic element according to claim 11, wherein X isselected from the group consisting of: ##STR82## wherein R₁₁ and R₁₂ areindependently H, alkyl, alkoxy, alkylthio, halo, carbamoyl, carboxy,amido, formyl, sulfonyl, sulfonamido or nitrile and R is a hydrogen atomor an unsubstituted or substituted alkyl group.
 13. A photographicelement according to claim 11, wherein X is selected from the groupconsisting of: ##STR83## wherein Z₁ is covalent bond, S, O, Se, NR, CR₂,CR═CR or CH₂ CH₂ and R is a hydrogen atom or a substituted orunsubstituted alkyl group.
 14. A photographic element according to claim11, wherein X has the structure: ##STR84## wherein Z₂ is S, O, Se, NR,CR₂ or CR═CR, and R₁₃ is an unsubstituted or substituted alkyl or arylgroup, and R₁₄ is a hydrogen atom or an unsubstituted or substitutedalkyl or aryl group and R is a hydrogen atom or a substituted orunsubstituted alkyl group.
 15. A photographic element according to claim1 or claim 2, wherein X is of formula (III): ##STR85## wherein: W is O,S or Se;Ar is an aryl group or a heterocyclic group; R₈ is R, carboxyl,NR₂, (OR)_(n), or (SR)_(n) ; n is 1-3 R₉ and R₁₀ are independently R orAr'; R₉ and Ar can be linked to form 5- to 8- membered ring; Ar' is anaryl group or a heterocyclic group; and R is a hydrogen atom or anunsubstituted or substituted alkyl group.
 16. A photographic elementaccording to claim 15, wherein X is selected from the group consistingof: ##STR86## wherein n is 1-3, and R is a hydrogen atom or anunsubstituted or substituted alkyl group.
 17. A photographic elementaccording to claim 1 or claim 2, wherein X is of formula (IV): ##STR87##wherein "ring" represents a substituted or unsubstituted 5-, 6- or7-membered unsaturated ring.
 18. A photographic element according toclaim 17, wherein X is selected from the group consisting of ##STR88##wherein Z₃ is O, S, Se or NR; R₁₅ is OR or NR₂ ; R₁₆ unsubstituted alkylor substituted alkyl and R is a hydrogen atom or an unsubstituted orsubstituted alkyl group.
 19. A photographic element according to claim 1or claim 2, wherein Y is:(1) X', where X' is an X group as defined instructures I-IV and may be the same as or different from the X group towhich it is attached (2) ##STR89## (3) ##STR90## where M=Si, Sn or Ge;and R'=alkyl or substituted alkyl; or (4) ##STR91## where Ar"=aryl orsubstituted aryl, and wherein structures I-IV are: ##STR92## wherein: mis 0 or 1; Z is O, S, Se or Te; Ar is an aryl group or a heterocyclicgroup; R₁ is R, carboxyl, amide, sulfonamide, halogen, NR₂, (OH)_(n),(OR')_(n) or (SR)_(n) ; where R' is alkyl or substituted alkyl; n is1-3; R₂ is R or Ar'; R₃ is R or Ar'; R₂ d R₃ together can form 5- to 8-membered ring; R₂ and Ar can be linked to form 5- to 8- membered ring;R₃ and Ar can be linked to form 5- to 8- membered ring; Ar' is an arylgroup or a heterocyclic group; and R is a hydrogen atom or anunsubstituted or substituted alkyl group; ##STR93## wherein: Ar is anaryl group or a heterocyclic group; R₄ is a substituent having a Hammettsigma value of -1 to +1; R₅ is R or Ar'; R₆ is R or Ar'; R₇ is R or Ar';R₅ and Ar can be linked to form 5- to 8- membered ring; R₆ and Ar can belinked to form 5- to 8- membered ring, in which case R₆ can comprise ahetero atom; R₅ and R₆ can be linked to form 5- to 8- membered ring; R₆and R₇ can be linked to form 5- to 8- membered ring; Ar' is an arylgroup or a heterocyclic group; and R is a hydrogen atom or anunsubstituted or substituted alkyl group; ##STR94## wherein: W is O, Sor Se; Ar is an aryl group or a heterocyclic group; R₈ is R, carboxyl,NR₂, (OR)_(n), or (SR)_(n) ; n is 1-3 R₉ and R₁₀ are independently R orAr'; R₉ and Ar can be linked to form 5- to 8- membered ring; Ar' is anaryl group or a heterocyclic group; and R is a hydrogen atom or anunsubstituted or substituted alkyl group; and ##STR95## wherein "ring"represents a substituted or unsubstituted 5-, 6- or 7-memberedunsaturated ring.
 20. A photographic element according to claim 19,wherein Y is COO⁻, Si(R')₃ or X'.
 21. A photographic element accordingto claim 20, wherein Y is COO⁻ or Si(R')₃.
 22. A photographic elementaccording to claim 1 or claim 2, wherein Z-(L-XY)_(k) is a compound ofthe formula: ##STR96##
 23. A photographic element according to claim 22wherein Z-(L-XY)_(k) is a compound of the formula:
 24. A photographicelement according to claim 1 or claim 2, wherein the emulsion layerfurther contains a sensitizing dye.
 25. A photographic element accordingto claim 24 wherein the sensitizing dye is selected from the groupconsisting of cyanine dyes, complex cyanine dyes, merocyanine dyes,complex merocyanine dyes, styryl dyes, oxonol dyes, hemioxonol dyes andhemicyanine dyes.
 26. A photographic element according to claim 1 orclaim 2, comprising a plurality of layers wherein one or more of thelayers of the element contains a hydroxybenzene compound.
 27. Aphotographic element according to claim 26, wherein the hydroxybenzenecompound has the formula: wherein V and V' each independently represent--H, --OH, a halogen atom, --OM (where M is alkali metal ion), an alkylgroup, a phenyl group, an amino group, a carbonyl group, a sulfonegroup, a sulfonated phenyl group, a sulfonated alkyl group, a sulfonatedamino group, a carboxyphenyl group, a carboxyalkyl group, a carboxyaminogroup, a hydroxyphenyl group, a hydroxyalkyl group, an alkylether group,an alkylphenyl group, an alkylthioether group, or a phenylthioethergroup.
 28. A photographic element according to claim 1 or claim 2,wherein the fragmentable electron donor compound Z-(L-XY)_(k) is addedto the emulsion layer after exposure.